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Ohm's law
Beginner
Voltage is proportional to current for ohmic conductors.
V = IRFor many conductors the current is proportional to voltage: V = IR with constant R at fixed temperature. Materials obeying this are ohmic.
12 V across 4 Ω: 3 A.
Diodes, filament lamps and thermistors are not ohmic.
In more detail
Ohm's law states that the current through a conductor is proportional to the voltage across it, V = IR, provided the temperature is constant. The constant R is the resistance.
Real-world uses
- Choosing resistors to limit current through LEDs.
- Electrical engineers use Ohm's law to design every circuit.
- Electronics designers use Ohm's law to choose a resistor that limits the current through an LED to a safe value.
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Frequently asked questions
Does every component obey Ohm's law?
No. Diodes and lamps do not, since their resistance changes with voltage or temperature.
What is an ohmic conductor?
One whose current is proportional to voltage at constant temperature.
Does every component obey Ohm's law?
No. Diodes and lamps have non-linear behaviour, so the voltage is not proportional to the current for them.
Related topics in Current Electricity & Circuits
Electric current · Direction of current · Drift velocity · Resistance · Resistivity · Conductivity