Power: Current and Resistance (GCSE Physics)
Power: Current and Resistance
Power
Using Current and Resistance
We can also calculate power using current and resistance. Let us look at the first equation, P = VI.
If we don’t know the voltage, but we only know the resistance and current, we can still work out the power.
We know that P = VI, and from before we know that V = IR. We can substitute IR in the place of V, to give P = (IR)I = P = I² R.
Where:
- power, P, in watts, W
- current, I, in amperes, A (amp is acceptable for ampere)
- resistance, R, in ohms, Ω
Question: Katie is using her PlayStation 4. It has a power rating of 920 watts and uses a current of 4 amps. Calculate the resistance of the PlayStation.
1. Write out the equation.
For this question, we actually need to rearrange the equation to make resistance the subject of the formula.
P = I² R
R = P / I²
2. Substitute in the numbers.
Now that we have the equation, we can substitute in the numbers.
R = P / I²
R = 920 / (4)²
R = 920 / 16
R = 57.5 Ohms
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