Electricity & Power Flashcards

All 6 cards in this deck

What is the equation linking electrical power, current and potential difference?

power (W) = current (A) × potential difference (V), $P = I \times V$

What is the equation linking electrical power, current and resistance?

power (W) = (current)$^2$ (A$^2$) × resistance (Ω), $P = I^2 \times R$

How does the power transfer in a circuit device depend on the current and the potential difference?

Power is the current multiplied by the p.d., so increasing either increases the power transferred.

What are the steps to find the current in a device from its power and the p.d. across it?

e.g. a $60\,\mathrm{W}$ lamp on a $12\,\mathrm{V}$ supply

1. Write $P = I \times V$
2. Rearrange: $I = P / V$
3. Substitute: $I = 60 / 12 = 5\,\mathrm{A}$

What are the steps to find the resistance of a component from its power and the current in it?

e.g. $20\,\mathrm{W}$ dissipated with a current of $2\,\mathrm{A}$

1. Write $P = I^2 \times R$
2. Rearrange: $R = P / I^2$
3. Substitute: $R = 20 / 4 = 5\,\Omega$

True or false? Doubling the current in a fixed resistor doubles the power dissipated.

False. $P = I^2R$, so doubling the current makes the power four times greater.