Thermal capacity (heat capacity)Copy

Learning Objectives

• Relate a rise in the temperature of a body to an increase in its internal energy
• Give a simple molecular account of an increase in internal energy
• Show an understanding of what is meant by the thermal capacity of a body
• Recall and use the equation thermal capacity = mc
•  Define specific heat capacity
•  Describe an experiment to measure the specific
  heat capacity of a substance
• Recall and use the equation
  change in energy = mcΔT

Contents to learn

Thermal capacity

Thermal capacity or heat capacity

It is defined as “the amount of heat needed to rise the temperature of the body by 1 oC”.

Thermal capacity = mass * specific heat capacity

Thermal capacity = m * C

Thermal capacity is measured in J / oC.

Specific heat capacity

The specific heat capacity of a substance is the heat required to produce a change of 1oC in 1Kg.

It is represented by C.

Specific heat capacity ( C ) = Heat received or given / mass * temperature change

C = Q / ( m * Δ T)

The unit of specific heat capacity is J / (Kg oC).

Experiment – Determination of specific heat capacity

To measure the specific heat capacity of a solid material , take a block of solid.

Drill two holes in to the block, one for thermometer and one for an electrical heater.

The heater is enclosed to ensure that it does not actually touch the block.

The amount of energy given by an electrical heater can be found by using the following relation

E = V * I * t ————————– (1)

Or

E = P * t —————————– (2)

In formula (1), V is the voltage , I is the electric current , and t is the time for which the electric heater is switched on.

In formula (2), P is the power of heater and t is the time for which the electric heater is switched on.

Change in temperature can be measured by taking the final and initial reading of the block with the help of the thermometer.

By determining the mass (m) of the block, we can calculate the specific heat capacity by using the relation

C = E / (m* ΔT)

To get the accurate result of specific heat capacity, the surface of the block can be covered with some thermal insulation.