Q.1. (A) Choose the correct alternative. (5 Marks)
(i) Alkaline earth metals have valency 2. This means that their position in the modern periodic table is in _______.
(A) Group 2
(B) Group 16
(C) Period 2
(D) d-block
(A) Group 2
(B) Group 16
(C) Period 2
(D) d-block
Answer: (A) Group 2
(ii) When the positive charge on an atom or an ion increases or the negative charge on them decreases it is called _______.
(A) Reduction
(B) Oxidation
(C) Displacement
(D) Decomposition
(A) Reduction
(B) Oxidation
(C) Displacement
(D) Decomposition
Answer: (B) Oxidation
(iii) _______ device is used to produce electricity.
(A) Electric motor
(B) Galvanometer
(C) Electric generator
(D) Voltmeter
(A) Electric motor
(B) Galvanometer
(C) Electric generator
(D) Voltmeter
Answer: (C) Electric generator
(iv) Light changes its direction when going from one transparent medium to another transparent medium. This is called the _______ of light.
(A) Reflection
(B) Dispersion
(C) Refraction
(D) Absorption
(A) Reflection
(B) Dispersion
(C) Refraction
(D) Absorption
Answer: (C) Refraction
(v) Height of the High earth orbit from the surface of the earth is _______.
(A) = 20,000 km
(B) = 27,000 km
(C) < 30,780 km
(D) > 35,780 km
(A) = 20,000 km
(B) = 27,000 km
(C) < 30,780 km
(D) > 35,780 km
Answer: (D) > 35,780 km
Q.1. (B) Answer the following questions. (5 Marks)
(i) Find the odd one out: Fuse wire, bad conductor, rubber gloves, generator.
Answer: Generator.
Reason: Generator is a device that produces electricity, whereas the others (fuse wire, bad conductor, rubber gloves) are related to safety or insulation properties in an electric circuit.
Reason: Generator is a device that produces electricity, whereas the others (fuse wire, bad conductor, rubber gloves) are related to safety or insulation properties in an electric circuit.
(ii) Complete the co-relation.
Red light wavelength close to 700 nm : Violet light wavelength close to : _______
Red light wavelength close to 700 nm : Violet light wavelength close to : _______
Answer: 400 nm
(iii) Match the pair:
Group 'A': Farsightedness
Group 'B': (a) Faraway object can be seen clearly (b) Nearby object can be seen clearly (c) Faraway object cannot be seen clearly
Group 'A': Farsightedness
Group 'B': (a) Faraway object can be seen clearly (b) Nearby object can be seen clearly (c) Faraway object cannot be seen clearly
Answer: Farsightedness — (a) Faraway object can be seen clearly
(iv) Write the electronic configuration of 'Aluminium'.
Answer: The atomic number of Aluminium is 13.
Electronic Configuration: 2, 8, 3
Electronic Configuration: 2, 8, 3
(v) State true or false: The escape velocity on the moon is less than that on the earth.
Answer: True.
Q.2. (A) Give scientific reasons (any two). (4 Marks)
(i) Sodium is always kept in kerosene.
Answer:
- Sodium is a highly reactive metal.
- It reacts vigorously with oxygen and moisture present in the air even at room temperature.
- This reaction is highly exothermic and can catch fire.
- To prevent this reaction and accidental fire, sodium is kept immersed in kerosene, as it does not react with kerosene and sinks in it.
(ii) We cannot clearly see an object kept at a distance less than 25 cm from the eye.
Answer:
- The ciliary muscles adjust the focal length of the eye lens to see objects at different distances (power of accommodation).
- However, there is a limit to how much the ciliary muscles can contract to increase the curvature of the lens.
- The minimum distance at which the eye can focus clearly without strain is called the Near Point or Least Distance of Distinct Vision, which is approximately 25 cm for a normal human eye.
- Therefore, if an object is placed closer than 25 cm, the eye cannot focus on it sharply, and the image appears blurred.
(iii) Tungsten metal is used to make a solenoid type coil in an electric bulb.
Answer:
- The filament of an electric bulb needs to generate intense light by becoming very hot (incandescence) without melting.
- Tungsten has a very high melting point ($3422^{\circ}C$).
- It does not melt even at the high temperatures required to emit light.
- Therefore, tungsten is used to make the solenoid-type coil (filament) in electric bulbs.
Q.2. (B) Answer the following questions (any three). (6 Marks)
(i) An object takes 5 seconds to reach the ground from a height of 5 m on a planet. What is the value of 'g' on the planet?
Given:
Time ($t$) = 5 s
Displacement ($s$) = 5 m
Initial velocity ($u$) = 0 m/s (assumed starting from rest)
To find: Gravitational acceleration ($g$)
Formula: $s = ut + \frac{1}{2}gt^2$
Calculation:
$$5 = (0 \times 5) + \frac{1}{2} \times g \times (5)^2$$
$$5 = 0 + \frac{1}{2} \times g \times 25$$
$$5 = 12.5 \times g$$
$$g = \frac{5}{12.5}$$
$$g = 0.4 \, m/s^2$$
Answer: The value of 'g' on the planet is 0.4 m/s².
Time ($t$) = 5 s
Displacement ($s$) = 5 m
Initial velocity ($u$) = 0 m/s (assumed starting from rest)
To find: Gravitational acceleration ($g$)
Formula: $s = ut + \frac{1}{2}gt^2$
Calculation:
$$5 = (0 \times 5) + \frac{1}{2} \times g \times (5)^2$$
$$5 = 0 + \frac{1}{2} \times g \times 25$$
$$5 = 12.5 \times g$$
$$g = \frac{5}{12.5}$$
$$g = 0.4 \, m/s^2$$
Answer: The value of 'g' on the planet is 0.4 m/s².
(ii) An element has its electronic configuration as 2, 8, 2. Now answer the following questions:
(a) What is the atomic number of this element?
(b) To which period does this element belong?
(a) What is the atomic number of this element?
(b) To which period does this element belong?
Answer:
(a) The atomic number is the sum of electrons: $2 + 8 + 2 = 12$.
(b) The element has 3 shells (K, L, M), so it belongs to the 3rd Period.
(a) The atomic number is the sum of electrons: $2 + 8 + 2 = 12$.
(b) The element has 3 shells (K, L, M), so it belongs to the 3rd Period.
(iii) Complete the following reaction and give name of products:
$CuSO_{4(aq)} + Fe_{(s)} \longrightarrow ......... + .......$
$CuSO_{4(aq)} + Fe_{(s)} \longrightarrow ......... + .......$
Answer:
Reaction: $CuSO_{4(aq)} + Fe_{(s)} \longrightarrow FeSO_{4(aq)} + Cu_{(s)}$
Names of products: Ferrous sulphate (Iron(II) sulphate) and Copper.
Reaction: $CuSO_{4(aq)} + Fe_{(s)} \longrightarrow FeSO_{4(aq)} + Cu_{(s)}$
Names of products: Ferrous sulphate (Iron(II) sulphate) and Copper.
(iv) Define specific heat of an object. Write its SI and CGS units.
Definition: The amount of heat energy required to raise the temperature of a unit mass of an object by $1^{\circ}C$ is called the specific heat of that object.
SI Unit: Joule per kilogram degree Celsius ($J/kg^{\circ}C$)
CGS Unit: Calorie per gram degree Celsius ($cal/g^{\circ}C$)
SI Unit: Joule per kilogram degree Celsius ($J/kg^{\circ}C$)
CGS Unit: Calorie per gram degree Celsius ($cal/g^{\circ}C$)
(v) Draw the electron-dot structure of methane ($CH_4$) and Ethane ($C_2H_6$).
Answer:
(Note: In an exam, you must draw the circles sharing electrons. Here is the structural representation.)
1. Methane ($CH_4$): Carbon shares 1 electron with 4 Hydrogen atoms.
Structure: Carbon in center, 4 Hydrogens surrounding it. Each C-H bond represents a pair of shared electrons (one dot from C, one cross/dot from H).
2. Ethane ($C_2H_6$): Two Carbon atoms share a pair of electrons between them. Each Carbon also shares electrons with 3 Hydrogen atoms.
Structure: $H_3C - CH_3$.
(Note: In an exam, you must draw the circles sharing electrons. Here is the structural representation.)
1. Methane ($CH_4$): Carbon shares 1 electron with 4 Hydrogen atoms.
Structure: Carbon in center, 4 Hydrogens surrounding it. Each C-H bond represents a pair of shared electrons (one dot from C, one cross/dot from H).
2. Ethane ($C_2H_6$): Two Carbon atoms share a pair of electrons between them. Each Carbon also shares electrons with 3 Hydrogen atoms.
Structure: $H_3C - CH_3$.
Q.3. Answer the following questions (any five). (15 Marks)
(i) Explain the concept 'escape velocity' in detail.
Answer:
- When an object is thrown vertically upwards, its velocity decreases due to the earth's gravitational downward pull.
- If the initial velocity is increased, the object reaches a greater height before falling back.
- There exists a specific initial velocity such that the object can overcome the earth's gravitational force completely and never fall back to earth.
- This specific initial velocity is called the Escape Velocity ($v_{esc}$).
- Formula: $v_{esc} = \sqrt{\frac{2GM}{R}}$, where G is the gravitational constant, M is the mass of the earth, and R is the radius of the earth.
- For Earth, the escape velocity is approximately 11.2 km/s.
(ii) Answer the following sub-questions regarding the modern periodic table:
(a) Write modern periodic law.
(b) Write the number of periods and groups.
(c) What is the valency of halogens?
(a) Write modern periodic law.
(b) Write the number of periods and groups.
(c) What is the valency of halogens?
Answer:
(a) Modern Periodic Law: "Properties of elements are a periodic function of their atomic numbers."
(b) There are 7 Periods (horizontal rows) and 18 Groups (vertical columns).
(c) The valency of halogens (Group 17) is 1.
(a) Modern Periodic Law: "Properties of elements are a periodic function of their atomic numbers."
(b) There are 7 Periods (horizontal rows) and 18 Groups (vertical columns).
(c) The valency of halogens (Group 17) is 1.
(iii) State whether the following reactions are endothermic or exothermic:
(a) $HCl + NaOH \to NaCl + H_2O + Heat$
(b) $2KClO_{3(s)} \to 2KCl_{(s)} + 3O_2 \uparrow$
(c) $CaO + H_2O \to Ca(OH)_2 + Heat$
(a) $HCl + NaOH \to NaCl + H_2O + Heat$
(b) $2KClO_{3(s)} \to 2KCl_{(s)} + 3O_2 \uparrow$
(c) $CaO + H_2O \to Ca(OH)_2 + Heat$
Answer:
(a) Exothermic (Heat is released/produced).
(b) Endothermic (Decomposition of Potassium Chlorate requires heat absorption).
(c) Exothermic (Formation of Slaked Lime releases heat).
(a) Exothermic (Heat is released/produced).
(b) Endothermic (Decomposition of Potassium Chlorate requires heat absorption).
(c) Exothermic (Formation of Slaked Lime releases heat).
(iv) Identify figure and write one use of it.
(Referring to the image of the Galvanometer in the paper)
Identification: The device shown is a Galvanometer.
Use: It is used to detect the presence of small electric currents in a circuit or to measure the direction of current (e.g., in electromagnetic induction experiments).
Identification: The device shown is a Galvanometer.
Use: It is used to detect the presence of small electric currents in a circuit or to measure the direction of current (e.g., in electromagnetic induction experiments).
(v) How much heat energy is necessary to raise the temperature of 5 kg of water from $20^{\circ}C$ to $100^{\circ}C$? ($c=1~kcal/kg^{\circ}C$)
Given:
Mass ($m$) = 5 kg
Change in temperature ($\Delta T$) = $100^{\circ}C - 20^{\circ}C = 80^{\circ}C$
Specific heat ($c$) = $1~kcal/kg^{\circ}C$
Formula: Heat Energy ($Q$) = $m \times c \times \Delta T$
Calculation:
$$Q = 5 \times 1 \times 80$$
$$Q = 400 \text{ kcal}$$
Answer: 400 kcal of heat energy is necessary.
Mass ($m$) = 5 kg
Change in temperature ($\Delta T$) = $100^{\circ}C - 20^{\circ}C = 80^{\circ}C$
Specific heat ($c$) = $1~kcal/kg^{\circ}C$
Formula: Heat Energy ($Q$) = $m \times c \times \Delta T$
Calculation:
$$Q = 5 \times 1 \times 80$$
$$Q = 400 \text{ kcal}$$
Answer: 400 kcal of heat energy is necessary.
(vi) Write the Cartesian sign convention for lenses.
Answer:
- The optical center (O) of the lens is taken as the origin. The principal axis is the X-axis.
- All distances are measured from the optical center.
- Distances measured in the direction of the incident light are taken as positive.
- Distances measured against the direction of the incident light are taken as negative.
- Distances measured vertically upwards from the principal axis are positive (height of object).
- Distances measured vertically downwards from the principal axis are negative (height of real image).
- Focal length of a convex lens is positive, while that of a concave lens is negative.
(vii) Complete the following chart regarding satellites (IRNSS, Weather, Earth's Observation).
Answer:
Based on the functions of Indian Satellites:
Based on the functions of Indian Satellites:
- IRNSS $\rightarrow$ Fixation of location (Navigation).
- INSAT / GSAT $\rightarrow$ Weather Study and Predict.
- IRS (Indian Remote Sensing) $\rightarrow$ Earth's Observation.
(viii) Give the chemical equations for the following reactions:
(a) Thermit reaction
(b) Burning of magnesium in air
(c) Iron nail/dust is dropped in aqueous solution of copper sulphate.
(a) Thermit reaction
(b) Burning of magnesium in air
(c) Iron nail/dust is dropped in aqueous solution of copper sulphate.
Answer:
(a) Thermit Reaction:
$$Fe_2O_{3(s)} + 2Al_{(s)} \longrightarrow 2Fe_{(l)} + Al_2O_{3(s)} + Heat$$
(b) Burning of Magnesium:
$$2Mg_{(s)} + O_{2(g)} \longrightarrow 2MgO_{(s)}$$
(c) Iron in Copper Sulphate:
$$Fe_{(s)} + CuSO_{4(aq)} \longrightarrow FeSO_{4(aq)} + Cu_{(s)}$$
(a) Thermit Reaction:
$$Fe_2O_{3(s)} + 2Al_{(s)} \longrightarrow 2Fe_{(l)} + Al_2O_{3(s)} + Heat$$
(b) Burning of Magnesium:
$$2Mg_{(s)} + O_{2(g)} \longrightarrow 2MgO_{(s)}$$
(c) Iron in Copper Sulphate:
$$Fe_{(s)} + CuSO_{4(aq)} \longrightarrow FeSO_{4(aq)} + Cu_{(s)}$$
Q.4. Answer the following (any one). (5 Marks)
(i) "A rainbow is the combined effect of the refraction, dispersion and total internal reflection of light." Prove this statement with the help of diagram and explain it.
Answer:
A rainbow is a natural spectrum appearing in the sky after a rain shower. It is indeed a combined effect of refraction, dispersion, and total internal reflection.
Mechanism:
(Note: In the exam, draw a circle representing a water droplet, show a ray entering, splitting, reflecting internally, and exiting as separate colors).
A rainbow is a natural spectrum appearing in the sky after a rain shower. It is indeed a combined effect of refraction, dispersion, and total internal reflection.
Mechanism:
- Refraction & Dispersion: When sunlight enters a water droplet suspended in the atmosphere, it gets refracted (bends) and dispersed. The sunlight separates into its component seven colors (VIBGYOR).
- Total Internal Reflection: These distinct colors strike the inner surface of the water droplet. If the angle of incidence is greater than the critical angle, the light undergoes total internal reflection inside the droplet.
- Refraction: Finally, the light gets refracted again as it comes out of the water droplet.
(Note: In the exam, draw a circle representing a water droplet, show a ray entering, splitting, reflecting internally, and exiting as separate colors).
(ii) Complete the following table (Homologous series of Alkanes).
Answer:
| Sr. No. | Name | Molecular Formula | Structural Formula (Condensed) |
|---|---|---|---|
| 1. | Methane | $CH_4$ | $CH_4$ |
| 2. | Ethane | $C_2H_6$ | $CH_3-CH_3$ |
| 3. | Propane | $C_3H_8$ | $CH_3-CH_2-CH_3$ |
| 4. | Butane | $C_4H_{10}$ | $CH_3-CH_2-CH_2-CH_3$ |
| 5. | Pentane | $C_5H_{12}$ | $CH_3-(CH_2)_3-CH_3$ |
| 6. | Hexane | $C_6H_{14}$ | $CH_3-(CH_2)_4-CH_3$ |
| 7. | Heptane | $C_7H_{16}$ | $CH_3-(CH_2)_5-CH_3$ |
| 8. | Octane | $C_8H_{18}$ | $CH_3-(CH_2)_6-CH_3$ |
| 9. | Nonane | $C_9H_{20}$ | $CH_3-(CH_2)_7-CH_3$ |
| 10. | Decane | $C_{10}H_{22}$ | $CH_3-(CH_2)_8-CH_3$ |
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