Page 122 - Physics - XI

Q8. What is the shape of cooling curve? (NCERT)
Ans. The cooling curve is an exponential decay curve (it is a hyperbolic curve).

Q9. Does the Newton's law of cooling hold good far all the temperature diff erences? (NCERT)
Ans. It should be noted that Newton's law of cooling holds good for the temperature diff erence between
the body and its surroundings which should not be more than 30°C. Hence, (θ – θ ) should not be
more than 30°C. 0

EXPERIMENT - 7

Aim
To determine specifi c heat capacity of a given solid by method of mixtures.

Apparatus and Materials Required

A hypsometer, calorimeter, stirrer, a lid and outer jacket, two half degree thermometers, given solid
(in powder form or in small pieces), physical balance, weight box, cold water, and clamp stand

Principle/Theory

Specifi c Heat Capacity
Specifi c heat capacity of a substance is defi ned as the amount of heat required to raise the temperature of

unit mass of substance through 1°C. In S.I. system, specifi c heat is measured in J kg K and in C.G.S.
–1
–1
system it is measured in cal g °C .
–1
–1
Principle of Calorimetry
According to this principle, "If the bodies at diff erent temperatures are brought in thermal contact, then the
amount of heat lost by the body at higher temperature is equal to the amount of heat gained by the body at
lower temperature, at equilibrium, provided that no heat is lost into the surroundings."
So, heat lost by the hotter body = heat gained by the colder body

Solid whose specifi c heat capacity is to be determined is heated uniformly up to a fi xed temperature in a
hypsometer. Then, it is fi lled in a calorimeter containing known quantity of cold water and the temperature
of mixture is recorded. The hot solid will lose heat whereas calorimeter and cold water will gain heat till
the temperature becomes same throughout.

If no heat is wasted otherwise, then
Heat lost by solid = Heat gained by colorimeter and cold water

Procedure
1. Place two thermometers in a beaker containing water. Note the readings of both the thermometers.

Keep thermometer A fi xed and fi nd the correction to be applied to thermometer B.
2. Pour suffi cient water in hypsometer. Put a small quantity of given solid in a copper tube of the hypsometer
and insert thermometer B in it. Now, add the remaining portion of solid so that the thermometer is
completely surrounded by solid. Place hypsometer on a burner.
3. Take a neat and clean calorimeter with a stirrer. Weigh it with the help of a physical balance. Now,
put a lid over it and weigh again.

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