# 4.08 Definitions of the terms relating to electrical potential.

## Circuit voltages.

There are two types of voltages in a circuit, e.m.f.s and voltage drops. There also several different terms used to describe voltages in electrical circuits, e.g. potential difference, voltage drop, etc. The difference between these various terms should be learned as you develop your understanding of electrical circuits. The list below defines these terms. Read through it briefly then use it for reference as needed.

• Electrical potential is a measure of the energy carried per coulomb of electrical charge.
• Voltage is the unit of measurement for electrical potential. The word voltage is also often used as an alternative term for electrical potential.
• A potential difference, is a difference in the electrical potential between two points in a circuit. This means that charged particles at these two points in the circuit, will have different electrical potentials and that a charged particle moving between these points, will experience an increase or reduction in potential.
• The potential difference across an e.m.f. is due to the energy being supplied by the e.m.f., as the charged particles move, between the terminals of the power supply.
• The potential difference across a resistor, is due to the charged particles loosing energy as they flow through the resistor. This energy is lost as heat. The resistor converts the electrical energy into heat.
• The term voltage drop or potential drop, is used to describe the potential difference that occurs across a resistor when current is flowing through it.
• The word voltage is often used when we should more correctly say voltage difference or potential difference. E.g. we may refer to a battery voltage being 9 volts, when we should say, a battery having a voltage difference (or potential difference) of 9 volts between its terminals. Obviously it is simpler just to refer to battery voltage and it is expected that engineers/physicists, will know that we are really referring to the voltage difference between the battery terminals.
• The symbol E or e is used in diagrams to represent an e.m.f. .
• The symbol V is generally used to represent a voltage drop, but it is sometimes used to represent any circuit voltage.
• The symbol v.d. is sometimes used to represent a voltage drop.
• The symbol p.d. can be used to represent any potential difference in a circuit.