The power *P* is equal to the voltage *V* times the current *I*:

*P* = *V* * *I*

The current *I* is equal to the voltage *V* divided by the resistance *R* (ohm's law)

*I* = *V* / *R*

Therefore the power *P* is equal to:

*P* = *V* * *V* / *R* = *V*^{2} / *R*

Therefore the resistance *R* in ohms (Ω) is equal to the square value of voltage *V* in volts (V) divided by the power *P* in watts (W):

*R*_{(Ω)} = *V*^{2}_{(V)} / *P*_{(W)}

Therefore ohms are equal to the square value of volts divided by watts:

Ohms = Volts^{2} / Watts

or

Ω = V^{2} / w

Find the resistance in ohms of a resistor given a voltage of 5 volts and a power of 2 watts.

The resistance R is equal to the square of 5 volts divided by 2 watts which is equal to 12.5 ohms.

*R* = (5V)^{2} / 2W = 12.5Ω

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