Electric circuits — Physical education, 14–17 years
Current is charge flowing through a complete path, while voltage is the energy transferred per unit of charge. The distinction explains why batteries, wires, and components work together.
Current and voltage
Electric current tells us how much charge passes a point each second, measured in amperes. Voltage tells us how much energy each coulomb can gain or lose, measured in volts. A circuit needs a complete conducting path and a source of voltage; a break stops the continuous flow.
Why separate the ideas?
A bright lamp does not simply mean “more electricity”. Its brightness depends on charge flow, energy per charge, and the lamp’s resistance. Scientists needed separate measurements to design reliable telegraphs, motors, and lighting, leading to circuit rules such as voltage = current × resistance.
Finding the current
A small heater has a resistance of 12 Ω and is connected to a 6 V battery. Start with Ohm’s law: V = I × R. Rearrange to I = V ÷ R, then substitute: I = 6 ÷ 12 = 0.5 A. Half an ampere flows through the heater in this simple circuit.
Current is not used up
It is easy to imagine that a lamp uses up current, like water disappearing into a sponge. The picture feels right because the lamp receives energy and becomes warm or bright. In a series circuit, the same current leaves the lamp; what changes is the energy carried by each charge, while some becomes light and heat.
Everyday electronic devices
Phone chargers, bicycle lights, kettles, and computers all rely on circuits that control current and voltage. Designers choose resistors, batteries, and switches so components receive safe amounts of energy. Household fuses and circuit breakers interrupt the path when the current becomes dangerously large.
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