Ohm's Law and V = IR

This lesson covers Ohm's law and the equation $V = IR$V=IR, as required by the Edexcel GCSE Combined Science specification (1SC0). You will learn what Ohm's law states, how to use and rearrange the equation, and the difference between ohmic and non-ohmic conductors.

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The Equation V = IR

The relationship between potential difference, current and resistance is:

$V = IR$V=IR

where:

• V = potential difference in volts (V)
• I = current in amperes (A)
• R = resistance in ohms ($\Omega$Ω)

This equation applies to any component in a circuit — it is the definition of resistance.

Rearranging

You will frequently need to rearrange this equation:

To find...	Rearranged form
Voltage (V)	$V = IR$V=IR
Current (I)	$I = \frac{V}{R}$I=RV​
Resistance (R)	$R = \frac{V}{I}$R=IV​

Exam Tip: Use a formula triangle to help you rearrange. Place V at the top, I at the bottom left and R at the bottom right. Cover the quantity you want to find — the remaining two show you the calculation.

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What Is Ohm's Law?