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REVISION NOTES POTENTIAL DIFFERENCE NATIONAL 5 If a charged particle is placed in an electric field, it experiences a force. This force makes the charged particle move. + We can produce an electric field by applying different voltages to two parallel metal plates. A battery produces an electric field in a wire. The electrons in the wire (charged particles) can then move. When a charged particle is moved by a field, it gains energy. The amount of energy it gains depends on the difference in voltage between the two plates, or between the two terminals of the battery. This is called the potential difference, though we often just call it ‘voltage’. So, potential difference is a measure of the energy given to charges in a circuit. What is a ‘volt’? A 3 V battery gives 3 joules of energy to each coulomb of charge that passes through it. A 12 V battery gives 12 joules of energy to each coulomb of charge that passes through it. So, one volt is the same as one joule per coulomb. 1 V = 1 J C-1 How the energy is used The greater the potential difference, the more energy is given to the charges in a circuit. As the charges move around the circuit, they give up their energy to bulbs, resistors and so on. The potential difference (voltage) across a resistor tells us how much energy is given up. If the p.d. across a resistor is 4 V, then 4 joules per coulomb are transferred to heat energy in the resistor.