Ohm’s Law



Currents, voltages and resistances in electric circuits may often be very small or very large — so multiples and submultiples are often used.

The voltage required applied to a 3.3 kΩ resistor to generate a current of 20 mA can be calculated as

Electric Resistance Nomogram

The default values in the nomogram above indicates 230 volts, resistance 24 ohm and current 10 amps.


Electric power can be expressed as

= U 2 / R (4)

P = electrical power (watts, W)

Example — Power Consumed

The power consumed in the 12V electrical circuit above can be calculated as

P = (12 volts) 2 / (18 ohm)

Example — Power and Electrical Resistance

A 100 W electric light bulb is connected to a 230 V supply. The current flowing can be calculated by reorganizing (4) to

The resistance can be calculated by reorganizing (4) to

Electric Power Nomogram

This nomogram can be used to estimate power vs. voltage and ampere.

The default values in the nomogram above indicates 240 volts, resistance 10 amps and power 2.4 kW for DC or single phase AC — and 4 kW for three phase AC.

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