Electronic circuits involve the manipulation of voltages, currents, and resistances. Knowing how these three properties relate to each other is a foundational part of circuit design. These relationships are described using the equation, Ohm’s Law.

The formula of Ohm’s Law is as follows:

V=I×RV = I × R


  • V = voltage expressed in Volts
  • I = current expressed in Amps
  • R = resistance expressed in Ohms

Note: Voltage is sometimes represented in Ohm’s Law using “E”

If two values are known, we can use algebra to reconfigure Ohm’s Law and calculate the third value:

To find the current, divide voltage by resistance.

I=V÷RI = V ÷ R

To find resistance, divide voltage by current.

R=V÷IR = V ÷ I

Schematic diagram with a voltage source and a resistor. The voltage of the voltage source is represented by V, the current through the loop is represented by I and the resistance of the resistor is represented by R

The above schematic has a voltage source with an unknown voltage. There is a current, I = 2A through a load resistor, R = 4.5Ω. Using Ohm’s Law we can find the voltage of the circuit’s voltage source:

V=I×RV = I × R
V=2A×4.5ΩV = 2A × 4.5Ω
V=9VV = 9V

The above example contains one voltage source and one load resistor. In general, a circuit’s load will consist of multiple components. In this case, you will need to find out how much of the source voltage is used by each component when applying Ohm’s Law.



Use the given values in Circuit 1 and Ohm’s Law to find the voltage (V) across the voltage source.

Type your answer below Answer 1. It should look like V = your answer


Use the given values in Circuit 2 and Ohm’s Law to find the current (I) through the circuit.

Type your answer below Answer 2. It should look like I = your answer


Use the given values in Circuit 3 and Ohm’s Law to find the resistance (R) of the resistor.

Type your answer below Answer 3. It should look like R = your answer

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