Page 147 - Physics - XI

ACTIVITY - 5

Aim

To study the factors aff ecting the rate of loss of heat of a liquid.

Apparatus and Materials Required

Two copper calorimeters of same size (one painted black and other highly polished, two copper thermometers
of diff erent sizes (one small and other big), two tumblers of same size (one metallic and other plastic), two
thermometers, stopwatch, cardboard lids for calorimeters, two laboratory stands, measuring cylinder, pan
to heat water, and plastic mug

Principle/Theory

The rate of loss of heat can be given by,

dQ = ms dθ
dt dt
Where, m = mass
s = specifi c heat capacity
θ = temperature
So, rate of loss of heat is directly proportional to rate of change of temperature,

dQ dθ
i.e. ∝
dt dt
The rate of loss of heat of a body depends upon the following factors:
(i) Area of the surface losing heat

(ii) Nature of the surface losing heat
(iii) Temperature diff erence between the hot body and its surroundings
(iv) Material of the container

Procedure

(i) Eff ect of area of surface on rate of loss of heat
1. Note the least count of the stopwatch and the two thermometers. Also, note the room temperature.
2. Heat water in the pan up to 80°C.

3. Pour 100 mL of hot water in the big Clamp stand
calorimeter (say A) and also in the T A T B
small calorimeter (say B) using a Lid with holes
measuring cylinder and a plastic mug A Lid with holes
with the least time loss. B

4. With the help of a laboratory stand,
suspend a thermometer in both the
calorimeters in such a way that the bulb Water
of the thermometer is dipped properly
in the hot water. Fig. 5.1: Experimental set up to study the
eff ect of surface area on rate of cooling

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