Physics (school) · Part 06
Electric circuits
How current, voltage and resistance work together in simple circuits.
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- Electric currentThe flow of charge round a circuit, measured in amperes (A). Charge = current x time.
- Potential differenceThe energy transferred per unit of charge as it moves between two points, measured in volts (V). It is what pushes the current round.
- ResistanceHow much a component opposes current, measured in ohms. A larger resistance means a smaller current for the same voltage.
- Ohm's lawV = I x R. Potential difference (V) equals current (A) times resistance (ohms). For a fixed resistor at steady temperature, current is proportional to voltage.
- Series circuitsComponents in one single loop. The current is the same everywhere. The supply voltage is shared between the components. Total resistance is the sum of the resistors.
- Parallel circuitsComponents on separate branches. The voltage across each branch is the same as the supply. The current splits between branches and rejoins. Adding branches lowers the total resistance.
- Electrical powerThe rate at which energy is transferred by a circuit. Power = potential difference x current (P = VI), or P = I squared x R. It is measured in watts (W).
- Circuit symbols and componentsStandard symbols draw circuits. A cell or battery supplies voltage. A resistor limits current. A diode lets current flow one way only. An LDR's resistance falls in light. A thermistor's falls as it gets hot.