Page 125 - Physics - XI

Q7. What is the relation between calorie and joule?
Ans. 1 calorie = 4.2 joule

Q8. What is water equivalent? (NCERT)
Ans. The water equivalent of a body is defi ned as the mass of the water which requires the same amount
of heat as required by the given body for the same increase of temperature.
Q9. What is thermal equilibrium? (NCERT)
Ans. Thermal equilibrium is a stage where the thermodynamical systems which are in equilibrium has the
same temperature.

Q10. Why do we generally use a calorimeter made of copper?
Ans. We use a calorimeter made of copper because copper has very low value of specifi c heat. So, due to
this, a large increase in temperature takes place when some quantity of heat is supplied to it.

Q11. Is specifi c heat a constant quantity?
Ans. No, specifi c heat is not a constant quantity because it depends on the nature of the substance and its
temperature.

Q12. Why is it important to stir the contents before taking the temperature of mixture? (NCERT)
Ans. It is important to stir the contents before taking the temperature because when we record this
temperature, it is used in the form of calculation as per the principle of calorimetry. So, it is must to
stir the contents before taking the temperature of mixture.
Q13. What quantities can be measured with the help of a calorimeter?
Ans. Thermal capacity, water equivalent of calorimeter, and latent heat

COMPETENCY-BASED QUESTIONS
COMPETENCY-BASED QUESTIONS
Multiple Choice Questions

Q1. The specifi c heat of water = 4200 J kg K and the latent heat of ice = 3.4 × 10 J kg . 100
–1
–1
5
–1
g of ice at 0°C is placed in 200 g of water at 25°C. The amount of ice that will melt as the
temperature of water reached 0°C is closed to (in grams)
a. 63.8 b. 69.3 c. 64.6 d. 61.7

Q2. In an experiment, a sphere of aluminium of mass 0.20 kg is heated up to 150°C. Immediately,
it is put into water of volume 150 cc at 27°C kept in a calorimeter of water equivalent to 0.0215
kg. Final temperature of the system is 40°C. The specifi c heat of aluminium is

(take 4.2 Joule = 1 calorie)

a. 378 J/kg°C b. 315 J/kg°C c. 476 J/kg°C d. 434 J/kg°C

Q3. A hot body obeying Newton's law of cooling is cooling down from its peak value 80°C to an
ambient temperature of 30°C. It takes 5 minutes in cooling down from 80°C to 40°C. How
much time will it take to cool down from 62°C to 32°C?

(Given ln 2 = 0.693, ln 5 = 1.609)
a. 3.75 minutes b. 8.6 minutes c. 9.6 minutes d. 6.5 minutes

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