ENERGY

Energy is measured in Joules (J) A joule is a small unit of energy

NOT JEWELS like these ->

JOULES

The amount of energy used over time is called POWER.

When describing POWER, we use Watts (W)

1 W = 1 Joule second

Watts are convenient to use for small things like light bulbs or laptops. However, energy used by larger devices may be described using kiloWatts (kW)

1 kW = 1000 W = 1000 Joules second

For devices that require large amounts of energy over a long period of time, like a house, one may use kiloWatt hours (kW●h) 1 kW ● h = 1000 W ● h = 1000 Joules x

hoursecond

An electric kettle is supplied with 100 000 J of energy and produces 90 000 J of useful heat energy. What is the efficiency of the electric kettle?

A man uses 150 J of energy moving a box up a steep slope. The amount of work produced is 37.5J. What is the percent efficiency of the man pushing the box?

A 55 inch plasma television uses 507 W when displaying High Definition TV.

What is the tv’s power use in kiloWatts?

A 55 inch plasma television uses 507 W when displaying High Definition TV.

How much energy does the TV use when watching TV for 30 minutes?

In Toronto, electricity costs $0.074 / kWh. An electric heater uses 2 kW every hour. How much would it cost to leave this heater on for 2 hours and 30 minutes?

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