# Physics - Power

> Source: https://ollybritton.com/notes/a-level/physics/topics/power/ · Updated: 2020-11-23 · Tags: physics, electricity, school, year-1

### Energy
##### What is power??
Power is the rate at which work is done.

##### What is the symbol formula for power??
$$
P = \frac{W}{t}
$$

##### If velocity is the rate of change of displacement, work done is??
The rate of change of energy.

##### What is the unit of power??
$$
\text{watt}, W
$$

##### What is the equation for power in terms of velocity??
$$
P = Fv
$$

##### How is efficiency calculated??
$$
\frac{\text{useful output energy}}{\text{total input energy}} \times 100%
$$

### 2021-02-03
##### If $$P = \frac{W}{t}$$ and $$W = VQ$$ How could you write the formula for $P$??
$$
P = \frac{VQ}{t}
$$

##### $$P = \frac{VQ}{t}$$ How could you rewrite this??
$$
P = IV
$$

##### What is electrical power??
The rate of energy transfer per component.

##### What are the units for power??
$$
W, \text{watts}
$$

##### If $$V = IR$$ and $$P = IV$$ How could you rewrite the power equation??
$$
P = I^2R
$$

##### If $$I = \frac{V}{R}$$ How could you rewrite the power equation??
$$
P = \frac{V^2}{R}
$$

##### Given a power, $P$, how can you calculate the work done $W$ over a given time $t$??
$$
W = Pt
$$

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