Home / Physics / Ohm’s law

Ohm’s law

How does the current change if you change the voltage? Design your own circuit, measure it, and find the rules.

    Physics · Electricity · Magnetism / Principles and Exploration

    Ohm’s law — principles and investigation

    If the resistance is constant and the voltage is increased, how much will the current increase? This is an Ohm's law experiment in which you design a circuit with a power supply, switch, ammeter, voltmeter, and resistor and directly record the measured values. After drawing a graph of voltage and current, change the resistance and compare the slopes of the two graphs.

    How does it work?

    If the resistance is constant, the current is proportional to the voltage. At the same voltage, the larger the resistance, the smaller the current. If you plot voltage on the horizontal axis and current on the vertical axis, the slope is the reciprocal of resistance, 1/R.

    Key relationship

    V = IR · I = V/R · P = VI

    Try this investigation

    1. Arrange the power supply, switch, ammeter, resistance, and voltmeter on the experimental bench to decorate the circuit and close the switch. Read the ammeter and voltmeter values ​​together and observe how the values ​​change when the voltage is changed.
    2. Set the resistance to 10 Ω, change the voltage to 2, 4, 6, 8, and 10 V and record the current. Before changing the voltage, make sure the circuit switch is closed.
    3. Change the resistance to 20 Ω and record again at a voltage of 2·4·6 V. Compare the current at the same voltage and the slope of the graph with voltage on the horizontal axis with the result for 10 Ω.

    Interpreting your results

    How will the slope of the voltage–current graph change if we change the resistance from 10 Ω to 20 Ω?

    If the horizontal axis is voltage and the vertical axis is current, the slope is 1/R. Since the resistance is doubled, the slope is halved and the current flowing at the same voltage is also halved.

    Assumptions and limitations

    Assume an ideal resistance and power supply whose resistance value does not change depending on temperature. It does not include the internal resistance of parts or instruments whose resistance varies depending on temperature, such as the filament of an actual light bulb, or the internal resistance of the power supply.