Power Flashcards

All 7 cards in this deck

What is the definition of power?

The rate at which energy is transferred, or the rate at which work is done.

What are the two equations for power?

$P = \dfrac{E}{t}$ and $P = \dfrac{W}{t}$ (energy transferred or work done ÷ time).

An energy transfer of 1 joule per second is equal to what power?

1 watt (W).

What are the steps to calculate the power of a device?
e.g. it transfers 600 J in 4 s

1. Write $P = \dfrac{E}{t}$
2. Substitute: $P = \dfrac{600}{4}$
3. $P = 150$ W

What are the steps to calculate the energy transferred by a device from its power?
e.g. a 50 W lamp left on for 20 s

1. Rearrange: $E = Pt$
2. Substitute: $E = 50 \times 20$
3. $E = 1000$ J

Two motors lift the same weight through the same height, but one takes less time. Which motor has the greater power output?

The faster one — it transfers the same energy in less time.

True or false? A device with a greater power output always transfers more energy in total.

False. It transfers energy at a faster rate; the total energy also depends on the time.