Beginner · 10 min
Voltage and energy per charge
Connect potential difference to energy transferred by electric charge.
Voltage compares energy per charge
Potential difference, often called voltage, is the energy transferred per unit charge between two points: V = E ÷ Q. One volt equals one joule per coulomb. Voltage is measured between points, while current describes charge flow through a point. A component with a 6 V potential difference transfers 6 J for each coulomb passing through it in the stated steady conditions.
Worked example
A component transfers 15 J as 3 C passes through it. Potential difference = 15 ÷ 3 = 5 V
Separate energy from charge
For a constant potential difference, energy transferred is E = V × Q. A supply gives energy to the circuit, and components transfer it into other forms. Charge remains conserved. Doubling the amount of charge passing through the same potential difference doubles the transferred energy; it does not require doubling the voltage. These exercises describe magnitudes for a device receiving energy.
Worked example
A steady 4 V is maintained across a component while 2 C passes through it. Energy transferred = 4 × 2 = 8 J
Compare energy per coulomb
- Calculate the energy transferred by 4 C passing through a constant potential difference of 3 V and then through 9 V.
- Explain how the same amount of charge can transfer different amounts of energy in these two cases.