Verification of joule's law (as $\Delta\theta \propto I^2$)

Apparatus

Lagged beaker or calorimeter with a lid, heating coil, battery or low voltage power supply, rheostat, ammeter or multimeter, thermometer, stopwatch, balance

Procedure

• Put sufficient water in a calorimeter to cover the heating coil. Set up the circuit as shown. Note the temperature.

• Switch on the power and simultaneously start the stopwatch. Allow a current of 0.5 A to flow for five minutes. Make sure the current stays constant throughout; adjust the rheostat if necessary.

• Note the current, using the ammeter.

• Note the time for which the current flowed.

• Stir and note the highest temperature. Calculate the change in temperature $\Delta\theta$.

• Repeat the above procedure for increasing values of current I, taking care not to exceed the current rating marked on the rheostat or the power supply. Take at least six readings.

• Plot a graph of $\Delta\theta$ (Y-axis) against $I^2$ (X-axis).

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Verification of joule's law (as $\Delta\theta \propto I^2$)

Results

$\theta_1/°C$	$\theta_2/°C$	$\Delta\theta/°C$	$I/A$	$I^2/A^2$

A straight-line graph through the origin verifies that $\Delta\theta \propto I^2$ i.e. Joule's law.