Concepts of Physics

IIT JEE Physics (1978-2018: 41 Years) Topic-wise Complete Solutions

Coffee Cup Calorimetry

Introduction

According to the laws of nature heat is transferred from a hot body to a cold body when they are brought in contact. The transfer of heat continues till they attain same temperature . The amount of heat loss incurred by the hot body is equal to the amount of heat gained by the colder body. This is also referred to as the Principle of Calorimetry.

In this experiment, a thermocol cup is used as a container to do the calorimetry and estimate the specific heat capacity of aluminium.

Apparatus

Coffee heater, thermocol cup, thermocol lid, aluminium block, water, weighing balance, thermometer.

Procedure

  1. Measure the mass of the aluminium block using the weighing balance and note its mass as \(M_{Al}\).
  2. Put the small aluminium block in normal tap water. Measure its temperature and note it as \(T_1\).
  3. Now fill the coffee cup with 100 ml of water and put the coffee heater in it and cover it. Put the thermometer in the cup from the hole in the thermocol lid. Switch on the heater. When the thermometer shows 70 degrr celsius (\(T_2\)), switch off the heater and remove it.
  4. Quickly take out the aluminium block from the normal tap water, wipe it and put it in the thermocol cup. Close the lid and stir the water with the thermometer. See the temperature of the thermometer falling till it becomes constant after some time. Note this temperature as \(T\).
  5. Using the formula of calorimetry find the specific heat capacity of aluminium

$$ M_{Al} S_{Al} (T-T_1) = M_w S_w (T_2-T) $$ Here \(M_w\) = Mass of 100 ml of water is 100 gram (density 1 gram/ml) and \(S_w\) = Specific heat of water is \(1\,\mathrm{cal/g/C}\).

Discussion

The specific heat capacity of Aluminium estimated by this method is close to the actual value. This is because thermocol is a poor conductor of heat and also it is very light (less mass) so the heat transfer occurs mainly between the water and the aluminium block.