Ohm’s law — Engineering, 14–17 years
How voltage, current and resistance set the behaviour of a simple electrical circuit. Engineering, 14–17 years.
The relationship
In a simple circuit, voltage is the push, current is the flow, and resistance makes that flow harder. Ohm’s law links them: voltage equals current multiplied by resistance. Change one of the three, and at least one of the others must change too.
Why engineers need it
A circuit can fail if too much current reaches a component: a wire may heat up or an LED may burn out. Engineers use Ohm’s law to choose a resistor, battery or wire before building. The relationship grew from measurements showing that many materials oppose current in a predictable way.
A resistor for an LED
A 9 V battery is connected to an LED that needs 2 V and 20 mA. The resistor must take the remaining 7 V. Convert 20 mA to 0.020 A. Then use R = V ÷ I: 7 ÷ 0.020 = 350 Ω. A real design would choose a nearby standard value and check its power rating.
Mixing the units
A common mistake is to put 20 into the formula instead of 0.020, because a label says 20 mA. That answer is not silly: milli- means one thousandth, and the prefix is easy to overlook. Convert every value to the units used by the formula before calculating.
Everyday electronics
Phone chargers, bicycle lights and sensor circuits all control current so components receive what they can handle. A designer may use Ohm’s law to limit an LED’s current or estimate how a battery will behave under load. It does not describe every component perfectly, especially ones with changing resistance.
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