Voltage and resistance — Physics, 11–13 years
Voltage provides the push that makes charge move, while resistance makes that movement harder. Together they help explain why different components in a circuit carry different currents.
Push and opposition in a circuit
Voltage is like a difference in electrical push between two points. Resistance is how strongly a component opposes moving charge. A larger voltage can drive more current, while a larger resistance usually allows less current through the same circuit.
Why measure both?
A battery label alone does not tell us how much current a lamp will use. The lamp’s resistance matters too. Scientists and engineers needed a way to predict brightness, heating and safe currents, so they measured voltage, current and resistance together.
A 6-volt lamp
A lamp has a resistance of 12 Ω and is connected to 6 V. Step 1: use current = voltage ÷ resistance. Step 2: 6 ÷ 12 = 0.5 A. Step 3: the circuit carries 0.5 amperes. If resistance rose to 24 Ω at the same voltage, current would fall to 0.25 A.
Voltage is not current
It is easy to treat voltage and current as two names for the same thing because both are measured in electrical circuits. They are different: voltage is the push between points, while current is the rate at which charge flows. Resistance links them but does not make them identical.
Choosing safe components
Phone chargers, bicycle lights and electronic toys need components that limit current. A resistor can protect a small light-emitting diode from too much current. Designers choose values so a device works brightly enough without overheating or damaging its parts.
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