Verifying Ohm’s Law Ohm’s Law is now well established as an accurate description of the relationship between voltage, current and resistance. However, we can still do experiments to check that Ohm’s Law is correct. When scientists carry out experiments to check that a law is correct the process is called verification. The circuit in Fig. 14 can be used to verify Ohm’s Law. A simpler version of this circuit is shown in Fig. 15.
Ammeter (measures current in amps) Voltmeter
(measures volts) Switch
Resistor Switch Power pack Variable resistor Resistor (heating element)
Fig. 15 The Ohm’s Law circuit, using symbols.
Fig. 14 Circuit used to demonstrate Ohm’s Law.
l l l l
l l
The voltmeter measures the voltage in the circuit. The ammeter measures the current in the circuit. The current is always in proportion to the voltage. When the voltage in the circuit is increased by using the dial on the power pack, it is found that the current also increases. The resistance caused by the heating element can be found by dividing any voltage value by its corresponding current value. A graph of voltage against current gives a straight line as shown in Fig. 16.
4 3 2 1
0.2 0.4 0.6 Current (amps)
Fig. 16 The graph of voltage against current is a straight line.
