காலப் பயணம்: வரமா? சாபமா? Time Travel Paradox: The Butterfly Effect Explained Through a Story

காலப் பயணம்: வரமா? சாபமா?
காலத்தின் எச்சரிக்கை

காலத்தின் எச்சரிக்கை (முன்னுரை)

கால இயந்திரம் என்பது மனிதக் கற்பனையின் உச்சம்; ஆனால், அதுவே மனிதகுலத்தின் அழிவுக்கும் காரணமாகலாம். அதன் சக்தி அளப்பரியது; ஆனால், அதைவிடவும் அளப்பரியது அது சுமந்துவரும் ஆபத்து. காலத்தின் ஓட்டத்தில் ஒரு சிறு கல்லை எறிந்தாலும், அது எதிர்காலத்தில் ஒரு பெரும் புயலையே உருவாக்கக்கூடும். இதை உணர்த்தும் ஒரு சிறு உதாரணத்தைக் காண்போம்.

கதிர் என்ற ஓர் இளைஞன் இருந்தான். அவனுக்கு ஒரு கால இயந்திரம் கிடைத்ததாகக் கற்பனை செய்துகொள்வோம். தன் தாத்தாவையும் பாட்டியையும் இழந்து ஒரு வாரமே ஆகியிருந்த நிலையில், அந்த இயந்திரம் அவனுக்கு ஒரு வரமாகத் தோன்றியது. அவர்களை மீண்டும் பார்க்க, அதுவும் அவர்களின் இளமைக்காலத்தில் சந்திக்க அவன் பேரார்வம் கொண்டான். கால இயந்திரத்தை ஐம்பது ஆண்டுகள் பின்னோக்கிச் செலுத்தினான்.

அவன் தற்போது வசிக்கும் வீடு, அவனது தாத்தா பாட்டியின் பூர்வீக வீடுதான். எனவே, அந்தப் பழைய காலத்து வீட்டில்தான் அவர்களும் வாழ்ந்திருப்பார்கள் என்ற நம்பிக்கையுடன் அங்குச் சென்றான். மறைந்திருந்து தன் தாத்தாவையும் பாட்டியையும் ஆவலுடன் கவனித்தான். அவனது பாட்டி, உறங்கச் செல்வதற்கு முன், ஒரு குவளைப் பாலுடன் வராண்டாவில் அமர்ந்து செய்தித்தாள் படித்துக்கொண்டிருந்த தாத்தாவிடம் அதைக் கொடுத்தார்.

தன் தாத்தாவையும் பாட்டியையும் இளமைப் பொலிவுடன் கண்டதும் கதிர் பெருமகிழ்ச்சியடைந்தான். அந்த நொடியில்தான் அந்த விபரீதம் நிகழ்ந்தது. எதிர்பாராத விதமாக, கதிரின் காலில் ஏதோ இடறியதுபோலிருக்க, அவன் தன்னையறியாமல், "அம்மா!" என்று கத்திவிட்டான்.

பட்டாம்பூச்சி விளைவு (Butterfly Effect)

அவன் கத்திய அடுத்த கணமே, அவன் அந்த உலகிலிருந்து மறைந்துபோனான்! ஆம், கதிர் என்ற அந்த இளைஞன் இந்த உலகில் பிறக்கவேயில்லை என்றாகிவிட்டது!

இது எவ்வாறு நிகழ்ந்தது? கதிர் எழுப்பிய அந்தச் சிறு ஒலி, அந்தச் சிறிய குறுக்கீடு, அன்று அவர்களுக்குள் நிகழ வேண்டியதை மாற்றிவிட்டது. தாத்தா சத்தத்தைக் கேட்டு வெளியே வந்தார். இந்த இடைப்பட்ட தாமதத்தால், கதிரின் தந்தையை உருவாக்க வேண்டிய குறிப்பிட்ட உயிரணு பின்தங்கியது. கதிரின் தந்தை பிறக்கவில்லை; அதனால் கதிரும் பிறக்கவில்லை.

காலச்சக்கரத்தில் நாம் செய்யும் ஒரு மிகச்சிறிய மாற்றம், ஒரு பட்டாம்பூச்சியின் சிறகடிப்பு ஏற்படுத்தும் தாக்கத்தைப்போல, பிற்காலத்தில் மிகப்பெரிய, கணிக்க முடியாத விளைவுகளை ஏற்படுத்திவிடும்.

காலம் எனும் பிரபஞ்ச ஆற்றலின் இந்த விசித்திரமான, அதே சமயம் அபாயகரமான தன்மையைப் பற்றி ஓரளவு புரிந்துகொண்டிருப்பீர்கள் என்று நம்புகிறேன்.

இனி, இதேபோன்றதொரு காலப் பயணத்தின் சிக்கலில் சிக்கும் கதிரின் கதைக்குள் செல்வோம்.

DOWNLOAD BOOK

About the Author

Amin Buhari, M.Com
OMTEX Classes

"The hands that once wrote on the blackboard are now creating a world of imagination on paper."

Original Source Material:

HSC Physics Question Bank Important for Board Exam 2026 - Rotational Dynamics to Semiconductors

OMTEX CLASSES

HSC PHYSICS IMPORTANT FOR BOARD EXAM 2026

QUESTION BANK 2026

CHAPTER 1: ROTATIONAL DYNAMICS

ONE MARKS QUESTIONS

1. Define UCM.
2. Do we need a banked road for a two wheeler?
3. What is the value of tangential acceleration in UCM?
4. Does the angle of banking depend on the mass of vehicle?
5. During ice ballets, while in the outer rounds, why do the dancers outstretch their arms and legs?
6. State the principle of conservation of angular momentum.
7. Why does a diver in a swimming pool bend his before diving?
8. Two bodies have their moment of inertia I and 2I respectively about their axis of rotation. If their kinetic energies of rotation are equal, then what is the ratio of their angular velocity?
9. State the formula for the moment of inertia of a circular ring about an axis passing through its centre.
10. State the formula for the moment of inertia of a uniform disc about an axis passing through its centre.
11. State the formula for the moment of inertia of a solid sphere about an axis passing through its centre.
12. Find the radius of gyration of a uniform disc about an axis perpendicular to its plane and passing through centre.

TWO MARKS QUESTIONS

1. What is banking of roads? Why curved roads are banked.
2. Distinguish between UCM and Non UCM.
3. Distinguish between centripetal force & centrifugal force.
4. Define circular motion. State characteristics of circular motion.
5. On what factors does the frequency of conical pendulum depend? Is it independent of some factors?
6. In vertical circular motion, is zero speed possible at the top (uppermost point)? Under what conditions?
7. Derive an expression for maximum safety speed with which a vehicle should move along a curved horizontal road?
8. Draw a diagram showing all components of forces acting on a vehicle moving along a curved banked road.
9. Derive an expression for minimum speed for a vehicle travelling inside a well of death of radius r.
10. Define moment of inertia. State its SI unit & dimension.
11. Why is it useful to define radius of gyration? OR Explain physical significance of radius of gyration. OR Define radius of gyration. Explain its physical significance.
12. A uniform disc and a hollow right circular cone have the same formula for their moment of inertia, when rotating about their central axes. Why is it so?
13. Define angular momentum. State its SI unit & dimension.
14. Obtain an expression for kinetic energy of rolling motion in the form \(\frac{1}{2} MV^2 [1+\frac{K^2}{R^2}]\)
15. State the conditions under which the theorem of parallel axes and perpendicular axes are applicable. State the respective mathematical expressions.
16. Derive an expression for maximum speed of a vehicle at the top of the convex over bridge.

THREE MARKS QUESTIONS

1. Derive an expression for kinetic energy of a rotating body.
2. Obtain an expression for torque acting on a body rotating with uniform angular acceleration.
3. Derive an expression that relates angular momentum with the angular velocity of a rigid body.
4. Discuss the interlink between translational, rotational and total kinetic energies of a rigid object that rolls without slipping.
5. Derive an expression for moment of inertia of a uniform disc about an axis passing through its center and perpendicular to its plane.
6. State & prove theorem of perpendicular axes.
7. A particle of mass m just completes the vertical circular motion. Derive the expression for the difference in tensions at the highest and the lowest points.

FOUR MARKS QUESTIONS

1. State and prove theorem of parallel axes.
2. What is conical pendulum? Obtain an expression for its time period.
3. Obtain an expression for maximum safety speed with which a vehicle can be safely driven along a curved banked road. OR Show that the angle of banking is independent of mass of vehicle. OR Obtain an expression for maximum speed with which a vehicle can be driven safely on a banked road. Show that the safety speed limit is independent of mass of vehicle.
4. Using energy conservation, derive the expressions for the minimum speeds at different locations along a vertical circular motion controlled by gravity.
5. A rigid object is rolling down an inclined plane. Derive an expressions for the acceleration along the track and the speed after falling through a certain vertical distance.

HSC Physics Board Papers with Solution

• Physics - March 2025 - English Medium View Answer Key
• Physics - March 2025 - Marathi Medium View Answer Key
• Physics - March 2025 - Hindi Medium View Answer Key
• Physics - March 2024 - English Medium View Answer Key Answer Key
• Physics - March 2024 - Marathi Medium View Answer Key
• Physics - March 2024 - Hindi Medium View Answer Key
• Physics - March 2023 - English Medium View Answer Key
• Physics - July 2023 - English Medium View Answer Key
• Physics - March 2022 - English Medium View Answer Key
• Physics - July 2022 - English Medium View Answer Key
• Physics - July 2021 - English Medium View Answer Key
• Physics - February 2020 - English Medium View Answer Key
• Physics - March 2013 View
• Physics - October 2013 View
• Physics - March 2014 View
• Physics - October 2014 View
• Physics - March 2015 View
• Physics - July 2015 View
• Physics - March 2016 View
• Physics - July 2016 View
• Physics - March 2017 View
• Physics - July 2017 View

CHAPTER 2: MECHANICAL PROPERTIES OF FLUIDS

ONE MARKS QUESTIONS

1. What is an incompressible fluid?
2. State Pascal’s law.
3. Define cohesive force.
4. Define surface film.
5. Define range of intermolecular force.
6. Define sphere of influence.
7. Define surface energy of a liquid.
8. How much amount of work is done in forming a soap bubble of radius r.
9. Define viscosity.
10. Define viscous force.
11. Why the surface tension of paints and lubricating oil is kept low?
12. What is the basis of Bernoulli’s principle?
13. Why is a low density liquid used as a manometric liquid in a physics laboratory?
14. Why does velocity increase when water flowing in broader pipe enters a narrow pipe?
15. Why does the speed of liquid increase and its pressure decrease through constriction in a horizontal pipe?

TWO MARKS QUESTIONS

1. State properties of ideal fluid.
2. Define pressure. State its SI unit and dimension.
3. Define surface tension. State its SI unit & dimension.
4. Why two or more mercury drops form a single drop when brought in contact with each other.
5. What is capillarity? Hence state its any two applications.
6. Define angle of contact. State the factors affecting the angle of contact.
7. Draw a neat labelled diagram for a liquid surface in contact with solid, when the angle of contact is acute.
8. Derive the relation between surface tension and surface energy. OR Show that the surface tension of a liquid is numerically equal to the surface energy per unit area.
9. Obtain an expression for capillary rise or fall using pressure difference method.
10. Derive an expression for pressure due to a liquid column.
11. Draw a neat & labelled diagram of hydraulic brakes.
12. State the effect of impurities on surface tension.
13. State the effect of temperature on surface tension.
14. Compare streamline flow & turbulent flow.
15. Define critical velocity and state the formula in terms of Reynolds number.
16. What is Reynolds number? What is its significance?
17. Define coefficient of viscosity. State its formula & SI unit.
18. State & explain Stokes law.

THREE MARKS QUESTIONS

1. Explain phenomenon of surface tension on the basis of molecular theory.
2. Draw & explain open tube manometer for the measurement of guage pressure.
3. Obtain an expression for capillary rise or fall using forces method.
4. Derive an expression for terminal velocity of a spherical object falling under gravity through a viscous medium.
5. Obtain an expression for conservation of mass starting from the equation of continuity.
6. Derive an expression for speed of a liquid flowing out through an orifice at a depth h below the free surface.(speed of efflux)

FOUR MARKS QUESTIONS

1. Derive an expression for excess pressure inside a drop. OR Derive expression for Laplace law for a spherical membrane of bubble due to surface tension.
2. Explain the capillary action.

CHAPTER 3: KINETIC THEORY OF GASES & RADIATION

ONE MARKS QUESTIONS

1. Mention the conditions under which a real gas obeys ideal gas equation.
2. State the formula for ideal gas equation.
3. On what factors do the degree of freedom depend?
4. What will happen to the mean square speed of the molecules of a gas if the temperature of the gas increase?

TWO MARKS QUESTIONS

1. Define athermanous substance & diathermanous substance.
2. Differentiate between ideal gas & real gas.
3. When gas is heated its temperature increases. Explain this phenomenon based on kinetic theory of gases.
4. State & explain Wein’s displacement law
5. Show that for a monoatomic gas the ratio of two specific heats is 5:3.
6. Show that for a diatomic gas the ratio of two specific heats is 7:5.
7. Two vessels A and B are filled with same gas where the volume, temperature and pressure in vessel A is twice the volume temperature and pressure in vessel B. Calculate the ratio of the number of molecules of the gas in vessel A to that in vessel B.
8. Explain on the basis of kinetic theory, how the pressure of gas changes if its volume is reduced at constant temperature.

THREE MARKS QUESTIONS

1. Show that RMS velocity of a gas molecules is directly proportional to square root of its absolute temperature
2. Show that average energy per molecule is proportional to the absolute temperature T of the gas.
3. Calculate the ratio of two specific heats of polyatomic gas molecule.
4. What is perfectly black body? How can it be realized in practice? OR What is perfectly black body? Explain Ferry’s black body.
5. Explain the construction & working of Ferry’s black body.
6. Explain the spectral distribution of blackbody radiation. OR Show graphical representation of energy distribution spectrum of perfectly black body.
7. State & prove Kirchhoff’s law of heat radiation.
8. State & prove Stefan-Boltzman law.
9. Define i) coefficient of absorption ii) coefficient of reflection and iii) coefficient of transmission.

FOUR MARKS QUESTIONS

1. Derive an expression for average pressure of an ideal gas.
2. Derive Mayer’s relation for molar specific heat of gases.
3. State the law of equipartition of energy and hence calculate molar specific heat of monoatomic and diatomic gases at constant volume and constant pressure.

CHAPTER 4: THERMODYNAMICS

ONE MARKS QUESTIONS

5. When two objects are said to be in thermal equilibrium?
6. State Zeroth law of thermodynamics.
7. What is thermodynamic process?
8. Give an example of some familiar process in which heat is added to an object, without changing its temperature.
9. Name the different macroscopic variables of system.
10. A gas contained in a cylinder surrounded by a thick layer of insulating material is quickly compressed. Has there been a transfer of heat?
11. What sets the limit on efficiency of a heat enegine?
12. Why should a Carnot cycle have two isothermal two adiabatic processes?
13. Define refrigeration.
14. In which thermodynamic process the total internal energy of system remains constant?

TWO MARKS QUESTIONS

9. Differentiate between reversible & irreversible process.
10. Draw P-V diagram showing positive work with varying pressure.
11. Draw a neat labelled energy flow diagram of heat engine.
12. Draw neat labelled diagram of schematic of refrigearator.
13. Explain cyclic process.
14. Write short note on free expansion in thermodynamic process.
15. What is a thermodynamic process? Give any two types of it.

THREE MARKS QUESTIONS

1. Explain the two different ways in which internal energy of a system can be changed.
2. Write short note on classification of thermodynamic system.
3. Write short note on thermodynamic equilibrium OR Define chemical equilibrium, mechanical equilibrium and thermal equilibrium.
4. Explain thermodynamics of a isothermal process. OR Derive an expression for the work done during an isothermal process.
5. Explain thermodynamics of a isobaric process.
6. Explain thermodynamics of a isochoric process.
7. A solar cooker and a pressure cooker both are used to cook food. Treating them as a thermodynamic system, discuss the similarities and difference between them.
8. What are the elements of heat engine?
9. Draw a PV diagram and explain the concept of positive and negative work done.
10. Explain the performance of a refrigerator with the help of energy flow diagram.
11. Explain heat addition during a thermodynamic process.

FOUR MARKS QUESTIONS

1. State first law of thermodynamics and derive the relation between the change in internal energy (\(\Delta U\)), work done(W) and heat (Q).
2. Explain the work done during a thermodynamic process.
3. Explain the thermodynamics of adiabatic process.

CHAPTER 5: OSCILLATIONS

ONE MARKS QUESTIONS

1. Define linear simple harmonic motion.
2. A simple pendulum is inside a space craft. What will be its periodic time?
3. What is amplitude of SHM.
4. State the formula for frequency of SHM in terms of force constant.
5. What does the phase of \(\pi/2\) indicates in linear SHM.
6. Define angular SHM.

TWO MARKS QUESTIONS

1. Derive differential equation of linear SHM.
2. Derive differential equation of angular SHM.
3. Show that SHM is a projection of UCM on any diameter.
4. Define second’s pendulum. Derive the formula for length of second’s pendulum.
5. State the formula for angular frequency and time period of damped oscillations.
6. Differentiate between free oscillation & forced oscillations.
7. Differentiate between conical pendulum & simple pendulum.

THREE MARKS QUESTIONS

1. Using differential equation of linear SHM, obtain the expression for (a) velocity in SHM (b) acceleration in SHM.
2. Obtain an expression for resultant amplitude of composition of two SHM’s having same period along same path.
3. Obtain an expression for period of simple pendulum performing SHM.
4. Obtain an expression for the period of a magnet vibrating in a uniform magnetic field performing SHM.
5. Derive differential equation for damped harmonic oscillations.
6. State the three laws of simple pendulum.
7. Draw the graphs of displacement, velocity and acceleration against phase angle, for a particle performing linear SHM from a) mean position b) positive extreme position.
8. Show that a linear SHM is the projection of a UCM along any of its diameter.
9. Define a) free oscillations b) forced oscillations c) resonance.

FOUR MARKS QUESTIONS

4. Using differential equation of linear SHM, obtain the expression for acceleration, velocity and displacement of SHM.
5. Deduce the expression for kinetic energy, potential energy and total energy of a particle performing SHM.

CHAPTER 6: SUPERPOSITION OF WAVES

ONE MARKS QUESTIONS

1. A wave is represented by an equation \(y= A \sin(Bx+Ct)\). Given that the constants A, B and C are positive, can you tell in which direction the wave is moving?
2. Why wave motion is doubly periodic?
3. What is interference of sound waves.
4. What are beats?
5. State any one characteristics of sound.
6. Define waxing & wanning.
7. State the formula for end correction of a pipe open at both ends.

TWO MARKS QUESTIONS

1. For a stationary wave set up in a string having both ends fixed, what is the ratio of the fundamental frequency to the third harmonic?
2. What are stationary wave? Why are they called stationary wave?
3. Distinguish between overtone & harmonic. OR What are harmonics and overtones.
4. Distinguish between stationary wave & progressive wave.
5. State the characteristics of progressive waves.
6. State the characteristics of stationary waves.
7. State any four applications of beats.
8. Draw a neat labelled diagram of experimental setup of sonometer.
9. Obtain the formula for end correction of a pipe open at both ends.
10. State the characteristics of sound.
11. Write short note on Quality or timbre.
12. Differentiate between free vibrations and forced vibrations.

THREE MARKS QUESTIONS

1. Find the amplitude of resultant wave produced due to interference of two waves given as \(y_1= A_1 \sin\omega t\) and \(y_2=A_2 \sin (\omega t+\phi)\)
2. Derive an expression for equation of stationary wave on a stretched string.
3. State and explain laws of vibrating strings.
4. Show that only odd harmonics are present in the vibrations of air column in a pipe closed at one end.
5. Prove that all harmonics are present in the vibrations of the air column in a pipe open at both ends.

FOUR MARKS QUESTIONS

1. Explain the formulation of stationary wave by analytical method. What are nodes and antinodes? Show that distance between two successive nodes or antinodes is \(\lambda/2\).
2. Explain the production of beats and deduce analytically the expression for beat frequency.
3. Explain reflection of transverse waves from denser medium.

CHAPTER 7: WAVE OPTICS

ONE MARKS QUESTIONS

1. What is the shape of the wavefront on earth for sunlight.
2. What is the shape of wavefront at a point far away from the source of light.
3. What is the relation between phase difference and optical path in terms of speed of light in vaccum.
4. What should be the ratio of slit width to the wavelength for a single slit illuminated by light of wavelength \(\lambda\).
5. Define plane of polarization.
6. Define resolving power of telescope.

TWO MARKS QUESTIONS

1. State Huygens principle? Draw a spherical wavefront using Huygen’s principle.
2. What are primary and secondary sources of light?
3. What is wavefront? How is it releted to rays of light?
4. What are the conditions for obtaining good interference pattern.(four)
5. What is meant by coherent sources? What are the two methods for obtaining coherent sources in the laboratory?
6. What is diffraction of light? How does it differ from interference?
7. What are Fraunhoffer and Fresnel diffractions?
8. Explain Rayleigh’s criterion for resolution.
9. What is optical length? How it is differ from actual path length?
10. State any two postulates of Newtons corpuscular theory.
11. Compare Young’s double slit interference pattern and single slit diffraction pattern.

THREE MARKS QUESTIONS

1. Derive the law’s of reflection of light using Huygen’s principle.
2. Derive the law’s of refraction of light using Huygen’s principle.
3. What is polarization? Derive Malus law.
4. What is Brewster law? Derive the formula for Brewster angle.
5. Describe Young’s double slit experiment with a neat diagram showing points of maximum and minimum intensity.
6. Explain experimental setup for Fraunhoffer diffraction with neat diagram.

FOUR MARKS QUESTIONS

1. Describe Young’s double slit interference experiment and derive conditions for occurrence of dark & bright fringes. Define fringe width & derive formula for it.
2. Derive the conditions for bright & dark fringes produced due to diffraction by a single slit.
3. What is interference? Explain constructive & destructive interference with the help of diagram.

CHAPTER 8: ELECTROSTATICS

ONE MARKS QUESTIONS

1. What will be the electric field intensity at the centre of charged conducting hollow sphere?
2. State the formula for giving the relation between electric field intensity & potential gradient.
3. State the formula for electric field intensity at a point outside an infinitely long charged cylindrical conductor.
4. What do you mean by dielectric polarization?
5. What is equipotential surface?
6. If the difference between the radii of the two spheres of a spherical capacitor is increased, state whether the capacitance will increase or decrease.
7. A metal plate is introduced between the plates of charged parallel plate capacitor. What is its effect on the capacitance of the capacitor?

TWO MARKS QUESTIONS

1. What are polar & non polar dielectrics?
2. Explain the principle of a capacitor.
3. Obtain an expression for the electric intensity at a point outside uniformly charged infinite plane sheet.
4. Obtain an expression for the electric field intensity at a point outside an infinitely long charged cylindrical conductor.
5. What are free charges & bound charges?
6. Draw a neat & labelled diagram of Van de Graff generator.

THREE MARKS QUESTIONS

1. Derive an expression for effective capacitance of three parallel plate capacitors connected in series.
2. Obtain an expression for energy stored in a charged condenser/ capacitor. Explain it in different forms.
3. Write principle & explain construction of Van de graff generator.
4. Derive an expression capacitance of a parallel plate capacitor without dielectric.

FOUR MARKS QUESTIONS

1. Obtain an expression for the potential energy of a dipole in an external field.
2. Derive an expression capacitance of a parallel plate capacitor with dielectric slab.
3. Derive an expression for the electric potential due to an electric dipole.

CHAPTER 9: CURRENT ELECTRICITY

ONE MARKS QUESTIONS

1. State Kirchhoff’s first (current) law.
2. State Kirchhoff’s second (voltage) law.
3. Are Kirchhoff’s laws applicable to both AC & DC circuits?
4. Define potential gradient
5. On what factor does the potential gradient of the wire depends?
6. What is the SI unit of potential gradient?
7. Why should not the jockey be sided along potentiometer wire?
8. On what factor does the internal resistance of cell depends?
9. What is the value of resistance for ideal ammeter.
10. Define shunt.
11. Define Galvanometer.

TWO MARKS QUESTIONS

1. Distinguish between potentiometer and voltmeter.
2. Define i) electrical circuit ii) junction
3. State any two possible sources of error in meter bridge experiment. How can they be minimized?
4. Explain the principle of potentiometer. OR Describe potentiometer.
5. Distinguish between ammeter and voltmeter.
6. State the uses of potentiometer. Why potentiometer is preferred over a voltmeter for measuring emf? OR state the advantages of potentiometer over voltmeter.
7. What are the disadvantages of potentiometer over voltmeter?
8. How will you convert moving coil galvanometer into ammeter?
9. How will you convert moving coil galvanometer into voltmeter?

THREE MARKS QUESTIONS

1. Explain with the help of neat circuit diagram, how will you determine the unknown resistance by using meter bridge.
2. Describe kelvin method to determine the resistance of galvanometer by using meter bridge.
3. Obtain the balancing condition in case of Wheatstone bridge.
4. Describe the use of potentiometer to compare the emfs of two cells by using individual cell method.

FOUR MARKS QUESTIONS

1. Describe with the help of a neat circuit diagram how will you determine the internal resistance of cell using potentiometer. Derive necessary formula.
2. Describe how potentiometer is used to compare emf of two cells by combination method.

CHAPTER 10: MAGNETIC FIELD DUE TO ELECTRIC CURRENT

ONE MARKS QUESTIONS

1. What is the value of force on a closed circuit in a magnetic field B?
2. What is the formula for magnetic force acting on a charged particle?
3. What is Lorentz force?
4. What is solenoid?
5. What is toroid?
6. State the orientation of magnetic dipole with respect to magnetic field, which possess maximum magnetic potential energy.

TWO MARKS QUESTIONS

1. Draw a neat and labelled diagram of suspended type moving coil galvanometer.
2. Derive an expression for magnetic force acting on straight wire carrying current.
3. State the formula for magnetic potential energy of a dipole and hence obtain the minimum and maximum magnetic potential energy.
4. With the help of suitable diagram state the expression for Biot Saverts law in vector form.
5. Derive the expression for magnetic field produced by the circular arc of wire.
6. What is cyclotron? State it’s principle of working.
7. Obtain an expression for magnetic field of a toroid.

THREE MARKS QUESTIONS

1. Explain cyclotron motion and cyclotron formula.
2. State & explain Ampere circuital law.
3. Obtain an expression for magnetic field inside a solenoid. OR Using Amperes law, derive an expression for the magnetic induction inside an ideal solenoid carrying a steady current.
4. Derive an expression for the net torque on a rectangular current carrying loop placed in a uniform magnetic field with its rotational axis perpendicular to the field.
5. Explain the construction and working of moving coil galvanometer. OR Show that current flowing through a moving coil galvanometer is directly proportional to the angle of deflection of coil.
6. Derive an expression for axial magnetic field produced by current in circular loop.

FOUR MARKS QUESTIONS

1. Show that currents in two long straight parallel wires exert forces on each other. Derive the expression for the force per unit length on each conductor.
2. Using Biot Saverts law, obtain an expression for the magnetic field near a straight infinitely long current carrying wire.

CHAPTER 11: MAGNETIC MATERIALS

ONE MARKS QUESTIONS

1. Which property of soft iron makes it useful for preparing electromagnet?
2. What happens to a ferromagnetic material when its temperature increases above curie temperature?
3. Give the formula for gyromagnetic ratio?
4. State the formula for the Bohr magnetron.
5. What does the ratio of magnetization to magnetic intensity indicates?
6. The relative permeability of medium is 0.075. What is its magnetic susceptibility?
7. State the formula for orbital magnetic moment of the revolving electron.

TWO MARKS QUESTIONS

1. Define magnetization. State its SI unit and dimension.
2. What is gyromagnetic ratio? Write necessary expression.
3. What is magnetic intensity and magnetic susceptibility?
4. Derive the relation between magnetic field intensity H and magnetization M for a magnetic material placed in magnetic field.
5. Differentiate between paramagnetic and ferromagnetic substance.
6. Differentiate between diamagnetic and paramagnetic substance.
7. Give any two point of difference between diamagnetic and ferromagnetic substance.
8. Draw the diagrams showing the dipole moments in a paramagnetic substance when external magnetic field is a) absent b) strong
9. Show that orbital magnetic dipole moment of a revolving electron is evr/2.
10. What should be retentivity and coercivity of a permanent magnet.
11. What does the hysteresis loop represents?
12. Explain one application of electromagnet.
13. Discuss Curie law for paramagnetic materials.
14. Calculate the gyro magnetic ratio of electron.

THREE MARKS QUESTIONS

1. Obtain an expression for orbital magnetic moment of an electron rotating about the nucleus in an atom.
2. Obtain the expression for Bohr magnetron.
3. Explain ferromagnetism on the basis of domain theory.
4. Derive an expression for period of angular oscillation of a bar magnet.

CHAPTER 12: ELECTROMAGNETIC INDUCTION

ONE MARKS QUESTIONS

1. What do you mean by electromagnetic induction?
2. A uniform magnetic field B, pointing upward fills a circular region of radius s in horizontal plane. If B changes with time, find the induced emf.
3. State the mathematical relation between number of turns in primary coil to secondary coil in step u transformer.
4. State Lenz’s law.
5. Define self-inductance.
6. What does the negative sign indicates in Lenz’s law?

TWO MARKS QUESTIONS

1. State Faraday’s Laws of electromagnetic induction.
2. Derive an expression for emf (e) generated in length (l) moving in uniform magnetic field (B) with uniform velocity (V) along x axis.
3. Derive an expression for energy stored in the magnetic field in terms of induced current.
4. What are eddy current? State applications of eddy currents.
5. Explain why inductance of two coils connected in parallel is less than the inductance of either coil.
6. Define Coefficient of self inductance. State its formula & SI unit.
7. Define mutual inductance. State its formula & SI unit.
8. Distinguish between step up and step down transformer.
9. What is transformer? State the working principle of transformer.
10. Define coefficient of coupling? State the formula for it.
11. State the formula for inductance in series & inductance in parallel.
12. Draw a neat labelled diagram of AC generator.
13. Derive an expression for motional emf in a rotating bar.

THREE MARKS QUESTIONS

1. State and explain Lenz’s law in the light of principle of energy.
2. Obtain an expression for the self-inductance of a solenoid.
3. Derive an expression for energy density of a magnetic field.
4. A long solenoid of length l, cross sectional area A and having \(N_1\) turns (primary coil) has a small coil of \(N_2\) turns (secondary coil) wound about its center. Determine the mutual inductance M of two coils.

FOUR MARKS QUESTIONS

1. With the help of suitable diagram describe working of transformer. Hence derive an expression for the ratio of emfs in terms of number of turns in primery and secondary coil.
2. Find an expression for power expended in pulling a conducting loop out of a magnetic field.

CHAPTER 13: AC CIRCUITS

ONE MARKS QUESTIONS

1. What is wattless current?
2. What is phasor?
3. For very high frequency AC supply, capacitor behaves like a pure conductor. Why?
4. State the formula for average value of alternating emf over full cycle.
5. State the formula for rms value of an alternating current over full cycle.
6. State the equation for impedance Z in the AC circuit.
7. What is the relation between average current and rms current over half cycle.
8. In LCR series circuit, what is the condition for current resonance?
9. Differentiate between series resonance circuit and parallel resonance circuit.
10. State the formula for power factor of an LCR circuit.
11. What is the value of power dissipated in purely resistance circuit?
12. What is the value of power dissipated in purely inductor circuit?
13. What is the value of power dissipated in purely capacitor circuit?
14. Define Q factor for resonance.
15. Define Average value of an alternating emf.

TWO MARKS QUESTIONS

1. What is the average or mean value of an alternating emf? Obtain the expression for it.
2. Compare resistance and reactance.
3. Draw a phasor diagram showing e and i in the case of purely inductive circuit.
4. Draw a phasor diagram showing e and i in the case of purely capacitive circuit.
5. What is the natural frequency of LC parallel resonant circuit? What is the reactance of this circuit at this frequency?
6. What is meant by impedance? State the formula for it in the case of LCR Circuit.
7. State any two characteristics of LCR series resonant circuit.
8. State any two characteristics of LC parallel resonant circuit.
9. Differentiate between series resonance circuit and parallel resonance circuit.
10. What is choke coil? State its uses?

THREE MARKS QUESTIONS

1. State the rms value of an alternating current? Write the relation between the rms value and peak value of an alternating current that varies with time.
2. Explain the terms a) inductive reactance b) capacitive reactance c) impedence
3. Obtain an expression for average power dissipated in a purely resistance AC circuit.
4. Show that in an AC circuit containing pure inductor, the voltage is ahead of current in phase by \(\pi/2\) rad.
5. When an AC source is connected to an ideal inductor show that the average power supplied by the source over a complete cycle is zero.
6. Prove that an ideal capacitor in an AC circuit does not dissipate power.
7. An emf \(e=e_0 \sin \omega t\) applied to a series LCR circuit derives a current \(i=i_0 \sin (\omega t \pm \phi)\) in the circuit. Deduce the expression for the average power dissipated in the circuit.
8. Explain electrical resonance in LC parallel circuit. Deduce the expression for the resonant frequency of the circuit.

FOUR MARKS QUESTIONS

1. An AC source generating a voltage \(e=e_0 \sin \omega t\) is connected to a capacitor of capacitance C. Find the expression for the current i through it. Plot graph of e and i versus \(\omega t\).
2. A device Y is connected across an AC source of emf \(e=e_0 \sin \omega t\). The current through Y is given as \(i=i_0 \sin (\omega t+\pi/2)\).
   a) Identify the device Y and write the expression for its reactance.
   b) Draw the graph showing variation of emf and current with time over one cycle of AC for Y.
   c) Draw phasor diagram for device Y.
3. Derive an expression for the impedance of an LCR circuit connected to an AC power supply.

CHAPTER 14: DUAL NATURE OF RADIATION AND MATTER

ONE MARKS QUESTIONS

1. What is photoelectric effect?
2. Can microwave be used in the experiment on photoelectric effect?
3. It is always possible to see the photoelectric effect with the red light?
4. Which metal will require the highest frequency of radiation to generate photocurrent?
5. State the importance of Davisson & Germer experiment.
6. Define photoelectrons.
7. Define photosensitive material.

TWO MARKS QUESTIONS

1. Define i) threshold frequency ii) threshold wavelength
2. Define i) Stopping potential or cut off potential ii) Photoelectric work function
3. Write four applications of photo cell.
4. What do you understand by the term wave particle duality? Where does it apply?
5. Explain the inverse linear dependence of stopping potential on the incident wavelength in a photoelectric effect experiment.
6. Explain how wave theory of light fails to explain the characteristics of photoelectric effect.
7. Draw a neat labelled circuit diagram of experimental set up of photoelectric effect.

THREE MARKS QUESTIONS

1. State Einstein’s photoelectric equation. Explain two characteristics of photoelectric effect on the basis of Einstein’s photoelectric equation.
2. Explain any three observations from the experiment on photoelectric effect.
3. Describe the construction of photoelectric cell.
4. Derive an expression for De Broglie wavelength.
5. What is de Broglie hypothesis? Obtain the relation for de Broglie wavelength.
6. With the help of labelled circuit diagram, describe the experiment to study the characteristics of photoelectric effect.

FOUR MARKS QUESTIONS

1. With a neat labelled diagram, describe the Davisson & Germer experiment in support of the concept of matter waves.
2. Explain De Broglie hypothesis.

CHAPTER 15: STRUCTURE OF ATOMS AND NUCLEI

One Marks Questions

1. What is the angular momentum of an electron in first excited state for hydrogen atom?
2. In which electromagnetic spectrum for hydrogen, does the Lyman series lies?
3. State the names of visible series in Hydrogen spectrum.
4. How much energy must be supplied to hydrogen atom, to free the electron in the ground state?
5. State the value of minimum excitation energy for hydrogen atom.
6. What is nuclear energy?
7. What is radioactivity?
8. What is mass defect?

Two Marks Questions

1. State the difficulties faced by Rutherford’s atomic model.
2. Derive an expression for the radius of \(n^{th}\) Bohr orbit of the electron in hydrogen atom. OR
3. Show that the radius of Bohr orbit is directly proportional to the square of the principle quantum number.
4. State any two limitations of Bohr’s atomic model.
5. With the help of a neat labelled diagram, describe the Geiger-Marsden experiment.
6. State Bohr seconds postulate for atomic model. Express it in its mathematical form.
7. Obtain an expression for decay law of radioactivity.
8. Define atomic number and mass number.
9. What are isotopes? Give one example.
10. What are isotones? Give one example.
11. Explain what are nuclear fission and nuclear fusion giving one example each.
12. What is the difference between nuclear reactor and nuclear bomb?
13. Explain nuclear binding energy.

Three Marks Questions

1. State the postulates of Bohr’s atomic model.
2. Derive the expression for the energy of an electron in the atom.
3. Define excitation energy, binding energy and ionization energy of an electron in an atom.
4. Obtain an expression for half life time of a radioactive material. Hence state the relation between average life and half life time of a radioactive material.
5. Show that for radioactive decay \(N(t)= N_0 e^{-\lambda t}\) , where symbols have their usual meaning.
6. What are alpha, beta and gamma decays and write down the formulae for the energies generated in each of these decays.
7. Starting from the formula for energy of an electron in the \(n^{th}\) orbit of hydrogen atom, derive the formula for the wavelengths of Lymen and Balmer series spectral lines.

Four Marks Questions

1. State the postulates of Bohr’s atomic model. Hence show energy of electron varies inversely to the square of principle quantum number.
2. Using the expression for the radius of orbit of Hydrogen atom, show that the linear speed varies inversely to principle quantum number n and the angular speed varies inversely to the cube of principle quantum number n.
3. Obtain an expression for wave number, when electron jumps from higher energy orbit to lower energy orbit.
4. Obtain an expression for decay law of radioactivity. Hence show that the activity \(A(t)=\lambda N_0 e^{-\lambda t}\)

CHAPTER 16: SEMICONDUCTOR DEVICES

ONE MARKS QUESTIONS

1. What is the purpose of capacitor filter circuit in a regulated power supply?
2. State advantages of full wave rectifier.
3. State any two special purpose diodes.
4. What is the need of rectification in regulatefd power supply?
5. On what factor does the wavelength of light emitted by a LED dpend?
6. Why should a photodiode be operated in reverse biased mode?
7. Why the base of a transistor mode is thin and is lightly doped?
8. Which method of biasing is used for operating transistor as an amplifier?
9. Give circuit symbol of a Zener diode.
10. State any two applications of Zener diode.
11. Draw a circuit symbol of PNP transistor or NPN transistor.

TWO MARKS QUESTIONS

1. Draw a neat and labelled circuit diagram of full wave rectifier using semiconductor diode.
2. Draw a neat labelled circuit diagram for transistor as common emitter amplifier.
3. State any two advantages and disadvantages of photodiode.
4. Draw a block diagram of a simple rectifier circuit with respective output waveform.
5. How zener diode is different than ordinary diode?
6. State the principle and uses of a solar cell.
7. Why do we need filters in a power supply?
8. Why is the emitter, the base and the collector of a BJT doped differently?

THREE MARKS QUESTIONS

1. Draw the circuit diagram of a half wave rectifier. Explain its working.
2. Explain the working of a LED.
3. Explain the construction and working of solar cell.
4. Explain the principle of operation of a photodiode.
5. Explain how Zener diode maintains constant voltage across a load. OR With the help of neat circuit diagram explain the use of Zener diode as a voltage regulator.
6. Explain the forward and reverse characteristics of a Zener diode.
7. What do you mean by a logic gate, a truth table and a Boolean expression?
8. What is logic gate? Write down the truth table and Boolean expression for AND gate.
9. What are the uses of logic gates? Why a NOT gate known as an inverter?
10. Write Boolean expression for (i) OR gate (ii) AND gate, and (iii) NAND gate.
11. Define \(\alpha\) and \(\beta\). Derive the relation between them.
12. Explain the working of PNP transistor.

FOUR MARKS QUESTION

1. Define rectifier. Draw a neat diagram of full wave rectifier and explain its working.
2. With the help neat circuit diagram, explain transistor as an amplifier.
3. Draw the circuit diagram to study the characteristics of transistor in common emitter mode. Draw the input and output characteristics.

ALL THE BEST FOR HSC 2024-25 BOARD EXAM

HSC Board 2026 Physics Important Definitions Class 12

HSC Board 2026

Imp Definitions for Board Exam 2026

1. ROTATIONAL DYNAMICS

(1) Uniform circular motion.

Ans. A particle is said to perform uniform circular motion if it moves in a circle or a circular arc at constant linear speed or constant angular velocity.

(2) Centripetal force.

Ans. In the uniform circular motion of a particle, the centripetal force is the force on the particle which at every instant points radially inward and produces the centripetal acceleration necessary to make the particle move in its circular path.

(3) Centrifugal force.

Ans. In the reference frame of a particle performing circular motion, centrifugal force is defined as a fictitious, radially outward force on the particle and is equal in magnitude to the particle's mass times the centripetal acceleration of the reference frame, as measured from an inertial frame of reference.

(4) Angle of banking.

Ans. Angle of banking is the angle of inclination of a banked road with the horizontal.

(5) Conical pendulum.

Ans. A conical pendulum is a simple pendulum whose bob revolves in a horizontal circle with constant speed such that the string describes the surface of a right circular cone.

(6) Moment of inertia.

Ans. The moment of inertia of a body about a given axis of rotation is defined as the sum of the products of the masses of the particles of the body and the squares of their respective distances from the axis of rotation.

(7) Radius of gyration.

Ans. The radius of gyration of a body rotating about an axis is defined as the distance between the axis of rotation and the point at which the entire mass of the body can be supposed to be concentrated so as to give the same moment of inertia as that of the body about the given axis.

(8) Angular momentum of a particle.

Ans. The angular momentum of a particle is defined as the moment of the linear momentum of the particle.

HSC Physics Board Papers with Solution

• Physics - March 2025 - English Medium View Answer Key
• Physics - March 2025 - Marathi Medium View Answer Key
• Physics - March 2025 - Hindi Medium View Answer Key
• Physics - March 2024 - English Medium View Answer Key Answer Key
• Physics - March 2024 - Marathi Medium View Answer Key
• Physics - March 2024 - Hindi Medium View Answer Key
• Physics - March 2023 - English Medium View Answer Key
• Physics - July 2023 - English Medium View Answer Key
• Physics - March 2022 - English Medium View Answer Key
• Physics - July 2022 - English Medium View Answer Key
• Physics - July 2021 - English Medium View Answer Key
• Physics - February 2020 - English Medium View Answer Key
• Physics - March 2013 View
• Physics - October 2013 View
• Physics - March 2014 View
• Physics - October 2014 View
• Physics - March 2015 View
• Physics - July 2015 View
• Physics - March 2016 View
• Physics - July 2016 View
• Physics - March 2017 View
• Physics - July 2017 View

2. MECHANICAL PROPERTIES OF FLUIDS

(1) Coefficient of viscosity.

Ans. The coefficient of viscosity of a fluid is defined as the viscous drag per unit area acting on a fluid layer per unit velocity gradient established in a steady flow.

(2) Angle of contact.

Ans. The angle of contact for a liquid-solid pair (a liquid in contact with a solid) is defined as the angle between the surface of the solid and the tangent drawn to the free surface of the liquid at the extreme edge of the liquid, as measured through the liquid.

(3) Pressure.

Ans. The pressure at a point in a fluid in hydrostatic equilibrium is defined as the normal force per unit area exerted by the fluid on a surface of infinitesimal area containing the point.

(4) Absolute pressure.

Ans. The absolute pressure, or total pressure, is measured relative to absolute zero on the pressure scale—which is a perfect vacuum—and is the sum of gauge pressure and atmospheric pressure. It is the same as the thermodynamic pressure.

(5) Gauge pressure.

Ans. Gauge pressure is the pressure exerted by a fluid relative to the local atmospheric pressure. Gauge pressure, \( p_g = p - p_0 \) where \( p \) is the absolute pressure and \( p_0 \) is the local atmospheric pressure.

(6) Range of molecular attraction or molecular range.

Ans. Range of molecular attraction is defined as the maximum distance between two molecules up to which the intermolecular force of attraction is appreciable.

(7) Sphere of influence.

Ans. The sphere of influence of a molecule is defined as an imaginary sphere drawn with the molecule as the centre and radius equal to the range of molecular attraction.

(8) Surface tension.

Ans. Surface tension of a liquid is defined as the tangential force per unit length, acting at right angles on either side of an imaginary line drawn on the free surface of the liquid.

(9) Surface energy.

Ans. Surface energy is defined as the extra (i.e., increased) potential energy of a liquid surface with an isothermal increase in the surface area.

(10) Velocity gradient in a steady flow.

Ans. In a steady flow of a fluid past a solid surface, the rate at which the velocity changes with distance within a limiting distance from the surface is called the velocity gradient.

(11) Volume flux.

Ans. The volume of fluid passing by a given point per unit time through an area is called the volume flux or volume flow rate.

(12) Mass flux.

Ans. The mass of fluid passing by a given point per unit time through an area is called the mass flux or mass flow rate.

3. KINETIC THEORY OF GASES AND RADIATION

(1) Coefficient of emission (emissivity) of a body.

Ans. Coefficient of emission (emissivity) of a body is defined as the ratio of the emissive power of the body to the emissive power of a blackbody at the same temperature as that of the body.

(2) Emissive power of a body.

Ans. Emissive power of a body at a given temperature is defined as the quantity of radiant energy emitted by the body per unit time per unit surface area of the body at that temperature.

(3) Mean free path.

Ans. The average distance travelled by a gas molecule between successive collisions, the average being taken over a large number of free paths (or collisions), is called the mean free path.

(4) Root mean square speed of gas molecules.

Ans. Root mean square speed of gas molecules is defined as the square root of the arithmetic mean of the squares of the speeds of all molecules of the gas at a given temperature.

(5) Molar heat capacity of a gas at constant volume.

Ans. Molar heat capacity of a gas at constant volume is defined as the quantity of heat required to raise the temperature of one mole of the gas through one degree (\(1^{\circ}\text{C}\) or 1 K), when its volume is kept constant.

(6) Molar heat capacity of a gas at constant pressure.

Ans. Molar heat capacity of a gas at constant pressure is defined as the quantity of heat required to raise the temperature of one mole of the gas through one degree (\(1^{\circ}\text{C}\) or 1 K), when its pressure is kept constant.

(7) Coefficient of absorption (Absorptance).

Ans. The coefficient of absorption (absorptance or absorptive power) of a body is defined as the ratio of the quantity of radiant energy absorbed by the body to the quantity of radiant energy incident on the body in the same time.

(8) Coefficient of reflection (Reflectance).

Ans. The coefficient of reflection (reflectance) of the surface of a body is defined as the ratio of the quantity of radiant energy reflected by the surface to the quantity of radiant energy incident on the surface in the same time.

(9) Coefficient of transmission (Transmittance).

Ans. The coefficient of transmission (transmittance) of a body is defined as the ratio of the quantity of radiant energy transmitted by the body to the quantity of radiant energy incident on the body in the same time.

4. THERMODYNAMICS

1. Internal energy.

Ans. Internal energy of a system is defined as the sum of the kinetic energies of the atoms and molecules belonging to the system, and the potential energies associated with the interactions between these constituents (atoms and molecules).

2. Zeroth law of thermodynamics:

If two systems are each in thermal equilibrium with a third system, they are also in thermal equilibrium with each other.

3. First law of thermodynamics :

According to the first law of thermodynamics, "the total energy of a system and surroundings remains constant when the system changes from an initial state to final state."

4. Second law of thermodynamics :

i. Kelvin-Planck statement: Heat \( Q_H \) cannot be taken out of a hot reservoir and used in its whole for labour W. It is necessary for \( Q_C \) to exhaust (give away) some of its heat to a cold reservoir. This rules out the development of an ideal heat engine.

ii. Clausius statement: Heat cannot transfer from a colder body to a warmer body unless some effort is made to do this. This rules out the creation of the ideal refrigerator.

5. Mechanical equilibrium:

When there are no unbalanced forces within the system and between the system and its surrounding, the system is in mechanical equilibrium.

6. Chemical equilibrium:

If there is no net chemical reaction between two thermodynamic systems in contact with each other then it is said to be in chemical equilibrium.

7. Thermal equilibrium:

Two systems are said to be in thermal equilibrium with each other if they are at the same temperature, which will not change with time.

8. Quasi-static process:

A quasi-static process is an infinitely slow process in which the system changes its variables (\( P, V, T \)) so slowly such that it remains in thermal, mechanical, and chemical equilibrium with its surroundings throughout.

9. Reversible processes:

A thermodynamic process can be considered reversible only if it possible to retrace the path in the opposite direction in such a way that the system and surroundings pass through the same states as in the initial, direct process.

10. Irreversible processes:

All natural processes are irreversible. Irreversible processes cannot be plotted in a PV diagram, because these processes cannot have unique values of pressure, the temperature at every stage of the process.

11. Isothermal process:

It is a process in which the temperature remains constant but the pressure and volume of a thermodynamic system will change.

12. Isobaric process:

A thermodynamic process that is carried out at constant pressure i.e., \( \Delta p = 0 \) is called the isobaric process.

13. Isochoric process:

A thermodynamic process in which the volume of the system is kept constant is called the isochoric process.

14. Adiabatic process:

It is defined as one in which there is no exchange of heat (q) between the system and surrounding during operations.

5. OSCILLATIONS

(1) Periodic motion.

Ans. A motion that repeats itself at definite intervals of time is said to be a periodic motion.

(2) Oscillatory motion.

Ans. A periodic motion in which a body moves back and forth over the same path, straight or curved, between alternate extremes is said to be an oscillatory motion.

(3) Linear simple harmonic motion.

Ans. Linear simple harmonic motion is defined as the linear periodic motion of a body in which the force on the body (or its acceleration) is always directed towards the mean position of the body and its magnitude is proportional to the displacement of the body from the mean position.

(4) Period or periodic time of SHM.

Ans. The time taken by a particle performing simple harmonic motion to complete one oscillation is called the period or periodic time of SHM.

(5) Frequency of SHM.

Ans. The number of oscillations performed per unit time by a particle executing SHM is called the frequency of SHM.

(6) Amplitude of SHM.

Ans. The magnitude of the maximum displacement of a particle performing SHM from its mean position is called the amplitude of SHM.

(7) Phase of SHM.

Ans. Phase of simple harmonic motion represents the state of oscillation of the particle performing simple harmonic motion (SHM), i.e., it gives the displacement of the particle and its direction of motion from the equilibrium position.

(8) Ideal simple pendulum.

Ans. An ideal simple pendulum is a heavy point mass suspended from a rigid support by a weightless, inextensible and twistless string, and set oscillating under gravity through a small angle in a vertical plane.

(9) Seconds pendulum.

Ans. A simple pendulum of period two seconds is called a seconds pendulum.

(10) Angular SHM.

Ans. Angular SHM is defined as the oscillatory motion of a body in which the restoring torque responsible for angular acceleration is directly proportional to the angular displacement and its direction is opposite to that of angular displacement.

11. Damped oscillations.

Ans. Oscillations of gradually decreasing amplitude in the presence of dissipative frictional forces are called damped oscillations.

6. SUPERPOSITION OF WAVES

(1) Progressive wave OR Travelling wave.

Ans. A progressive wave or a wave motion is a periodic or oscillatory disturbance in a medium or in vacuum which is propagated without any damping and obstruction from one place to another at a finite speed.

(2) Transverse progressive wave.

Ans. A progressive wave in which the vibration of the individual particles of the medium is perpendicular to the direction of propagation of the wave is called a transverse progressive wave.

(3) Longitudinal progressive wave.

Ans. A progressive wave in which the vibration of the individual particles of the medium is along the line of propagation of the wave is called a longitudinal progressive wave.

(4) Stationary wave OR Standing wave.

Ans. When two identical progressive waves, i.e., waves having the same amplitude, wavelength and speed, propagate in opposite directions through the same region of a medium, their superposition under certain conditions creates a stationary interference pattern called a stationary wave or a standing wave.

(5) Transverse stationary wave.

Ans. When two identical transverse progressive waves travelling in opposite directions along the same line superimpose, the resultant wave produced is called a transverse stationary wave.

(6) Longitudinal stationary wave.

Ans. When two identical longitudinal progressive waves travelling in opposite directions along the same line superimpose, the resultant wave produced is called a longitudinal stationary wave.

(7) Free vibrations.

Ans. Vibrations of a body, free to vibrate, when it is disturbed from its equilibrium position and left to itself are called free vibrations.

(8) Forced vibrations.

Ans. The vibrations of a body in response to an external periodic force are called forced vibrations.

(9) Resonance.

Ans. If a body is made to vibrate by an external periodic force, whose frequency is equal to the natural frequency (or nearly so) of the body, the body vibrates with maximum amplitude. This phenomenon is called resonance.

(10) Beats.

Ans. A periodic variation in loudness (or intensity) when two sound notes of slightly different frequencies are sounded at the same time is called beats.

(11) Period of beats.

Ans. The time interval between successive maxima or minima of sound at a given place is called the period of beats.

(12) Beat frequency.

Ans. The number of beats produced per unit time is called the beat frequency.

7. WAVE OPTICS

(1) Wavefront.

Ans. A wavefront is defined as a surface of all neighbouring points which receive light waves from a source at the same instant and are in the same phase.

(2) Wave normal.

Ans. A wave normal at a point on a wavefront is defined as a line drawn perpendicular to the wavefront in the direction of propagation of the wavefront.

(3) Plane of vibration.

Ans. The plane of vibration of an electromagnetic wave is the plane of vibration of the electric field vector containing the direction of propagation of the wave. Experiment shows that it is the electric field vector \( E \) which produces the optical polarization effects.

(4) Plane of polarization.

Ans. The plane of polarization of an electromagnetic wave is defined as the plane perpendicular to the plane of vibration. It is the plane containing the magnetic field vector and the direction of propagation of the wave.

(5) The Brewster angle OR the polarizing angle.

Ans. The Brewster angle or the polarizing angle for an interface is the angle of incidence for a ray of unpolarized light at which the reflected ray is completely plane polarized.

(6) Interference of light.

Ans. Interference of light is the phenomenon in which the superposition of two or more light waves produces a resultant disturbance of redistributed light intensity or energy.

(7) Diffraction of light.

Ans. Diffraction of light is the phenomenon of bending of light waves at an edge into the region of the geometrical shadow.

(8) Resolving power of an optical instrument.

Ans. The resolving power of an optical instrument is defined as the reciprocal of its limit of resolution which is the smallest linear or angular separation between two point objects which appear just resolved when viewed through the instrument.

(9) Resolving power of a microscope.

Ans. The resolving power of a microscope is defined as the reciprocal of the least separation between two closely-spaced points on an object which are just resolved when viewed through the microscope.

(10) Resolving power of a telescope.

Ans. The resolving power of a telescope is defined as the reciprocal of the angular limit of resolution between two closely-spaced distant objecl so that they are just resolved when seen through the telescope.

8. ELECTROSTATICS

(1) Electric potential difference.

Ans. The electric potential difference between two points in an electric field is defined as the work done per unit charge by an external agent against the electric force in moving an infinitesimal positive charge from one point to the other without acceleration.

(2) Electric potential.

Ans. The electric potential at a point in an electric field is defined as the work per unit charge that must be done by an external agent against the electric force to move without acceleration a sufficiently small positive test charge from infinity to the point of interest.

(3) The electronvolt.

Ans. The electronvolt (symbol, eV) is the increase in the kinetic energy of a particle with a charge equal in magnitude to the elementary charge \( e \) when the particle is accelerated through a potential difference of one volt.

(4) Electric potential gradient.

Ans. The rate of change of electric potential with distance in a specified direction is called the electric potential gradient in that direction.

(5) Electric polarization.

Ans. The electric polarization at every point within a dielectric is defined as the electric dipole moment per unit volume. It has the direction of the external electric field.

(6) Capacitance of a capacitor.

Ans. The capacitance of a capacitor is defined as the ratio of the charge on either conductor to the potential difference between the two conductors forming the capacitor.

9. CURRENT ELECTRICITY

1. Junction:

Any point in an electric circuit where two or more conductors are joined together is a junction

2. Loop:

Any closed conducting path in an electric network is called a loop or mesh.

3. Branch:

A branch is any part of the network that lies between two junctions.

4. Kirchhoff’s First Law: (Current law/ Junction law) :

The algebraic sum of the currents at a junction in an electrical network, is zero

5. Kirchhoff’s Second Law: (Voltage law )

The algebraic sum of the potential differences (products of current and resistance) and the electromotive forces (emfs) in a closed loop is zero.

6. Voltmeter :

A voltmeter is a device which is used for measuring potential difference between two points in a circuit.

7. Potentiometer:

Potentiometer is one such device which does not draw any current from the circuit.

8. Shunt:

Moving coil galvanometer is converted into an ammeter by connecting a low resistance in parallel with the galvanometer, which effectively reduces the resistance of the galvanometer. This low resistance connected in parallel is called as shunt (S).

9. Potential gradient:

With a potential difference applied across a uniform resistance wire, potential gradient along the wire is the potential difference (the fall of potential from the high potential end) per unit length of the wire.

10. MAGNETIC FIELDS DUE TO ELECTRIC CURRENT

(1) The ampere.

Ans. The ampere is that constant current which if maintained in two infinitely long straight parallel wires, placed one metre apart in vacuum, would cause each wire to experience a force per unit length of \( 2 \times 10^{-7} \) newton per metre.

(2) The SI unit of magnetic field/induction OR The tesla.

Ans. The SI unit of magnetic field/induction is the tesla. The magnitude of magnetic induction is said to be one tesla if a charge of one coulomb experiences a force of one newton when it moves at one metre per second in a magnetic field in a direction perpendicular to the direction of the field.

11. MAGNETIC MATERIALS

(1) Magnetization.

Ans. The magnetization of the material is defined as the net magnetic moment per unit volume of a material.

(2) Magnetic intensity.

Ans. The magnetic intensity is defined as the magnetic induction in an isotropic medium divided by the permeability of the medium.

12. ELECTROMAGNETIC INDUCTION

(1) Magnetic flux.

Ans. The magnetic flux through a given area in a magnetic field is defined as the total number of magnetic lines of force passing normally through that area.

(2) Electromagnetic induction.

Ans. Electromagnetic induction is the phenomenon of production of emf in a conductor or circuit due to the motion of the conductor in a magnetic field or by a changing magnetic flux through the circuit.

(3) Self induction.

Ans. The phenomenon of production of induced emf in a coil, due to the change of current in the same coil, is called self induction.

(4) Self inductance OR Coefficient of self induction.

Ans. The self inductance or the coefficient of self induction of a coil is defined as the emf induced in the coil per unit time rate of change of current in the same coil.

(5) The henry.

Ans. The self inductance of a coil is 1 henry if an emf of 1 volt is induced in the coil when the current through the same coil changes at the rate of 1 ampere per second.

(6) Mutual induction.

Ans. The phenomenon of production of induced emf in one coil due to changing current in a magnetically linked neighbouring coil is called mutual induction.

(7) Mutual inductance OR Coefficient of mutual induction.

Ans. The mutual inductance or the coefficient of mutual induction of two magnetically linked coils is equal to the flux linkage of one coil per unit current in the neighbouring coil.

13. AC CIRCUITS

(1) Inductive reactance.

Ans. The resistance offered by an inductor to the alternating current through it is called the inductive reactance.

(2) Capacitive reactance.

Ans. The resistance offered by a capacitor to the alternating current ilirough it is called the capacitive reactance.

(3) Impedance.

Ans. In an AC circuit containing resistance and inductance and/or capacitance, the effective resistance offered by the circuit is called impedance.

(4) Average or mean value of A.C.

Average or mean value of A.C. is the average of all values of the voltage (or current) over the one-half cycle.

14. DUAL NATURE OF RADIATION AND MATTER

(1) Threshold frequency.

Ans. The threshold frequency for a given metal surface is defined as the characteristic minimum frequency of the incident radiation below which no photoelectrons are emitted from that metal surface.

(2) Threshold wavelength.

Ans. The threshold wavelength for a given metal surface is defined as the characteristic maximum wavelength of the incident radiation above which no photoelectrons are emitted from that metal surface.

(3) Stopping potential.

Ans. The stopping potential is defined as the value of the retarding potential difference that is just sufficient to stop the most energetic photoelectrons from reaching the collector so that the photoelectric current in a photocell reduces to zero.

(4) Photoelectric work function.

Ans. The photoelectric work function of a metal is defined as the minimum photon energy that will eject an electron from the metal.

15. STRUCTURE OF ATOMS AND NUCLEI

(1) Stationary (stable) orbit.

Ans. In the Bohr model of a hydrogen atom, a stationary or stable orbit is defined as any of the discrete allowed orbits such that the electron does not radiate energy while it is in such orbits.

(2) Ground state of an atom.

Ans. Ground state of an atom is defined as the lowest stable energy state of the atom.

3. Excitation energy of an atomic electron.

Ans. The energy required to transfer an electron from the ground state to an excited state (a state of higher energy) is called the excitation energy of the electron in that state.

4. Binding energy of an atomic electron.

Ans. Binding energy of an electron in an atom is defined as the minimum energy that should be provided to an orbital electron to remove it from the atom such that its total energy is zero.

(5) Ionization energy of an atomic electron OR Ionization energy of an atom.

Ans. Ionization energy of an electron in an atom is defined as the minimum energy required to remove the least strongly bound electron from a neutral atom such that its total energy is zero.

(6) Radioactivity.

Ans. Radioactivity is the phenomenon in which unstable nuclei of an element spontaneously distintegrate into nuclei of another element by emitting \( \alpha \) particles, or \( \beta \) particles, accompanied by \( \gamma \)-rays.

(7) Half-life of a radioactive element.

Ans. The half-life of a radioactive element is defined as the average time interval during which half of the initial number of nuclei of the element disintegrate.

(8) Decay constant or disintegration constant.

Ans. The decay constant or disintegration constant of a radioactive element is defined as the ratio of the disintegration rate at an instant to the number of undecayed nuclei of the element present at that instant.

(9) Mean-life of a radioactive element.

Ans. The mean-life of a radioactive element is the average time for which the undecayed nuclei of the element exist before decaying. It is equal in the reciprocal of the decay constant of that element.

(10) Nuclear fission.

Ans. Nuclear fission is a nuclear reaction in which a heavy nucleus of an atom splits into two or more fragments of comparable size either spontaneously or when bombarded by a neutron, with the release of enormous amount of energy.

(11) Nuclear fusion.

Ans. Nuclear fusion is a type of nuclear reaction in which lighter atomic nuclei (of low atomic numbers) fuse to form a heavier nucleus (of higher atomic number) with the release of enormous amount of energy.

(12) Chain reaction.

Ans. A chain reaction is a self-multiplying nuclear fission process in which neutrons ejected in one nuclear fission strike neighbouring nuclei of fissile material and cause more fissions.

16. SEMICONDUCTOR DEVICES

(1) Depletion layer (region).

Ans. The depletion layer or depletion region is the region of the junction between a \( p \)-type layer and an \( n \)-type layer within a single semiconducting crystal which is depleted of free charge carriers.

(2) Barrier potential.

Ans. The barrier potential is defined as the electric potential difference across the depletion region of a \( p-n \)-junction.

(3) Rectification.

Ans. The process of converting an alternating voltage (or current) to a direct voltage (or current) is called rectification.