Experiment Overview

This experiment determines the specific heat capacity of a liquid using electrical heating and calorimetry. The electrical energy supplied to the liquid is measured and related to the resulting temperature rise using a graphical method.

What This Experiment Demonstrates

• Thermal energy transfer by electrical heating
• Relationship between energy supplied and temperature rise
• Determination of specific heat capacity using a graph

Apparatus Required

• Calorimeter with lid and insulation
• Liquid sample (e.g. water or oil)
• Immersion heater
• Power supply
• Ammeter and voltmeter
• Stopwatch
• Thermometer or temperature probe
• Balance
• Stirrer

Theory

When a liquid is heated electrically, the electrical energy supplied is converted into thermal energy. This energy causes an increase in the temperature of the liquid.

The thermal energy gained by a liquid of mass \( m \) and specific heat capacity \( c \) is given by:

\[Q = mc\Delta T\]

The electrical energy supplied by the heater is:

\[E = VIt\]

Assuming negligible heat loss to the surroundings, the electrical energy supplied is equal to the thermal energy gained:

\[VIt = mc\Delta T\]

This can be written in the linear form:

\[E = (mc)\Delta T\]

A graph of electrical energy supplied \( E \) against temperature rise \( \Delta T \) is therefore a straight line whose gradient is equal to \( mc \). The specific heat capacity \( c \) can then be determined.

Method

1. Measure the mass of the empty calorimeter.
2. Add the liquid and measure the total mass to determine the mass of the liquid.
3. Insert the immersion heater, thermometer, and stirrer into the calorimeter.
4. Record the initial temperature of the liquid.
5. Switch on the power supply and start the stopwatch.
6. Record the voltage and current supplied to the heater.
7. Stir the liquid continuously to ensure uniform temperature.
8. Record the temperature of the liquid at regular time intervals.
9. Switch off the heater after a suitable temperature rise is achieved.

Observations

Record the temperature of the liquid at known time intervals along with the corresponding electrical energy supplied. Calculate the temperature rise \( \Delta T \) from the initial temperature.

Calculations

• Calculate the electrical energy supplied using \( E = VIt \).
• Determine the temperature rise \( \Delta T \).
• Plot a graph of \( E \) (y-axis) against \( \Delta T \) (x-axis).
• Find the gradient of the best-fit straight line.
• Calculate the specific heat capacity using \( c = \dfrac{\text{gradient}}{m} \).

For guidance on plotting graphs and determining gradients accurately, visit our Graph Guide.

Result

The graph of electrical energy supplied against temperature rise is a straight line. The specific heat capacity of the liquid is obtained from the gradient of the graph.

Video Demonstration

Video courtesy of Physics Online (YouTube). Video used for educational purposes under YouTube’s embedding policy.