Potential Difference

The potential difference (p.d.) across a component is the energy transferred from electrical energy to other forms per unit charge passing through it, V = W/Q. It is measured in volts, where 1 V = 1 J C^-1.As charge carriers pass through a component such as a resistor or a lamp, they do work and lose electrical energy, which is transferred to heat or light. A p.d. of 1 V means that 1 J of energy is transferred for every coulomb of charge.Potential difference is measured with a voltmeter connected in parallel across the component. An ideal voltmeter has an infinite resistance, so it draws no current from the circuit.Rearranging the definition gives W = VQ. For example, when 5.0 C of charge passes through a lamp with a p.d. of 6.0 V across it, 30 J of energy is transferred.When an electron is accelerated through a p.d. V, it gains kinetic energy eV. The energy gained by an electron accelerated through 1 V is called the electronvolt, 1 eV = 1.6 × 10^-19 J.