# Worksheet: Power and Energy

In this worksheet, we will practice using the formula P = E/t to calculate the rate at which energy is transferred by a device given the amount of energy it transfers in a given time.

**Q2: **

Which of the following is the correct unit for power?

- AAmp
- BJoule
- CVolt
- DWatt
- ESecond

**Q4: **

A kettle is filled with water and turned on. It takes 3 minutes to boil the water, and the kettle is supplied with J of energy in this time. What is the power of the kettle?

**Q5: **

A 30 mW LED in an electronic circuit is left on for 2 hours. How much energy does it transfer to its environment over this time? Assume that the LED is efficient.

**Q6: **

How many watts are there in 1 megawatt?

**Q7: **

What is 34 kJ in joules?

**Q8: **

Engy wants to find out how much electrical power her television needs when it is on. She watches television for a few hours and records how much energy has been supplied to it every half hour. The graph shows her results.

How much energy has been supplied to the television after 3 hours?

What is the power of her television?

**Q9: **

What is 6700 kilowatts in megawatts?

**Q10: **

Which of the following is the correct formula for the energy transferred, , in a given time, , for an electrical appliance with a given power, ?

- A
- B
- C
- D
- E

**Q11: **

What is 50 MW in watts?

**Q12: **

A microwave is used for 5 minutes, during which time it is supplied with 180 kJ of energy. What is the power of the microwave?

**Q13: **

What is 24 MW in kilowatts?

**Q14: **

How many joules are there in 1 kilojoule?

**Q15: **

What is joules in kilojoules?

**Q16: **

A 60 W incandescent light bulb is left on for 30 seconds. How much energy is supplied to it over this time?

**Q17: **

Which of the following is the correct unit for energy?

- AVolt
- BWatt
- CAmpere
- DJoule
- ECoulomb