Worksheet Solutions: Calorimetry | Physics Class 10 ICSE PDF Download

Part A — Multiple Choice Questions

Q1. The SI unit of heat (energy) is:

(a) Calorie

(b) Joule

(c) Erg

(d) Watt
Answer: (b) Joule
Explanation: In science, energy (including heat) is measured in joules in the International System of Units. A calorie is another unit often used for heat (1 calorie ≈ 4.2 joules), an erg is a much smaller unit (in the CGS system), and watt is a unit of power, not energy.

Q2. When pure ice at 0°C melts to water at 0°C, the temperature of the mixture:

(a) Rises

(b) Falls

(c) Stays constant

(d) Becomes 100°C
Answer: (c) Stays constant
Explanation: During a change of state (melting or freezing), the supplied heat is used only to change the phase, not to change the temperature. This hidden heat is called latent heat. So the temperature remains constant at 0°C until all the ice melts.

Q3. The specific heat capacity of a substance tells us:

(a) Heat needed to raise the body’s temperature by 1°C

(b) Heat needed to raise 1 kilogram of the substance by 1°C

(c) Heat needed to melt 1 kilogram of the substance

(d) Heat released when water freezes
Answer: (b) Heat needed to raise 1 kilogram of the substance by 1°C
Explanation: Specific heat capacity is heat per unit mass per degree rise in temperature. Option (a) is heat capacity (for the whole body), while (c) and (d) refer to latent heat (heat for change of state).

Q4. Coastal places have a moderate climate mainly because water has:

(a) Low specific heat capacity

(b) High specific heat capacity

(c) No specific heat capacity

(d) High latent heat of vaporisation only
Answer: (b) High specific heat capacity
Explanation: Water needs a lot of heat to change its temperature. This slows down heating during the day and cooling at night, keeping coastal temperatures moderate.

Q5. Which statement about impurities is correct?

(a) Impurities increase the melting point

(b) Impurities decrease the melting point

(c) Impurities do not affect the melting point

(d) Impurities make the temperature jump to 100°C
Answer: (b) Impurities decrease the melting point
Explanation: Adding impurities (like salt to ice) lowers the melting point. That is why salt–ice mixtures feel extra cold and are used in freezing mixtures.

Part B — Short Answer Questions 

Q6. What is heat capacity? How is it different from specific heat capacity?
Answer:

• Heat capacity is the heat needed to raise the temperature of an entire object by 1°C. It depends on how much material is present.

• Specific heat capacity is the heat needed to raise 1 kilogram of a material by 1°C. It is a property of the material itself, independent of mass.
  Why this matters: Two objects of the same material but different sizes have different heat capacities, but the same specific heat capacity.

Q7. Why is a calorimeter made of copper?
Answer:

• Copper is a good conductor of heat, so it quickly reaches the same temperature as its contents.

• Copper has low specific heat capacity, so it absorbs very little heat itself and does not disturb measurements much.
  Result: We can accurately measure heat gained or lost by substances inside it.

Q8. Why do farmers flood fields during a cold night in winter?
Answer: Water has a high specific heat capacity, so it cools slowly and releases heat slowly. This helps keep the air and plants near the ground slightly warmer, protecting crops from frost damage.

Q9. Explain the principle of calorimetry (principle of mixtures).
Answer: When a hot object is mixed with a cold object in an insulated container, heat lost by the hot object equals heat gained by the cold object, until both reach the same temperature. No heat is exchanged with the surroundings in an ideal setup.

Q10. What is latent heat? Give one example.
Answer: Latent heat is the heat absorbed or released during a change of state without any change in temperature.
Example: Ice at 0°C absorbs latent heat to become water at 0°C; the temperature does not rise during melting.

Part C — Long Answer Questions

Q11. How much heat is required to raise the temperature of 200 grams of water from 25°C to 55°C? (Specific heat capacity of water = 4200 J per kg per °C)
Solution (stepwise):

1. Mass, m = 200 g = 0.2 kg

2. Change in temperature = 55 − 25 = 30°C

3. Formula: Heat, Q = mass × specific heat capacity × change in temperature

4. Q = 0.2 × 4200 × 30 = 25,200 joules
   Answer: 25,200 joules

Q12. Explain how impurities and pressure affect the melting and boiling points of substances. Give examples.
Answer:

• Effect of impurities: The presence of impurities lowers the melting point and raises the boiling point.

  • Example: Salt added to ice lowers its melting point (basis of freezing mixtures).

  • Example: Adding salt to water increases its boiling point, making cooking faster.

• Effect of pressure:

  • For substances like ice, which contract on melting, the melting point decreases with pressure.

  • For substances like wax, which expand on melting, the melting point increases with pressure.

  • For liquids, an increase in pressure raises the boiling point, while a decrease lowers it.
    Thus, both impurities and pressure directly influence phase change temperatures.

Q13:How much heat is required to melt 500 g of ice at 0°C into water at 0°C? (Specific latent heat of fusion of ice = 3.34 × 10⁵ J per kg)
Solution (stepwise):

1. Mass, m = 500 g = 0.5 kg

2. Formula: Heat, Q = mass × specific latent heat

3. Q = 0.5 × 3.34 × 10⁵ = 1.67 × 10⁵ joules
   Answer: 167,000 joules