Electric circuits — Physics, 14–17 years
How a complete path lets charge transfer energy through a circuit. Physics, 14–17 years.
The idea
An electric circuit is a complete path in which moving charge transfers energy from a source to components such as lamps or motors. Current tells us how much charge passes a point each second. Voltage is the energy transferred per unit of charge, while resistance describes how strongly a component opposes current.
Why we need it
A bulb does not light merely because two wires touch a battery; charge needs a continuous route through the component and back to the source. Circuit ideas were developed to make electrical effects predictable and controllable. They let us explain why a switch works, why components heat up, and why different connections behave differently.
Worked example
A 12 V supply is connected to a 6 Ω resistor. Ohm’s law is V = IR, so rearrange it to I = V ÷ R. Substituting gives I = 12 ÷ 6 = 2 A. The resistor transfers power P = VI = 12 × 2 = 24 W, meaning 24 joules of electrical energy are transferred each second.
The common trap
A common mistake is imagining that current gets used up by the first lamp in a series circuit. That seems logical because the lamp takes energy from the circuit and becomes less bright if another lamp is added. Charge is not used up, though: the same current passes through each series component, while the available voltage is shared.
Where it appears
Circuit principles appear in phone chargers, household wiring, sensors, speakers, and medical equipment. Parallel circuits allow separate lamps or appliances to keep working if one branch fails. Engineers choose resistance and power ratings so components carry safe currents instead of overheating or damaging the surrounding material.
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