21 st October

Power and electrical power

Objectives

Understand what power is.

Explain that the amount of electrical energy a device transforms depends on how long the appliance is switched on for and the rate at which the device transforms energy. Be able to calculate the cost of electrical energy used.

Keywords

: Efficiency, Power, Energy, Kilowatt, Kilowatt-hour 2 lessons

Power

• What is power?

• Power is the energy transferred in a certain time. • Power in Watts is the amount of Joules transferred in 1 second.

ENERGY POWER ¦ TIME

Power Demo

• Height x weight = energy Total height: Weight: Time for walk: Time for run: Energy for walk: Energy for run: Power walk: Power run: • Energy/time = power

Electrical Power

• In pairs: • Do questions from Milner Text book p 40 41 including the remember box.

• Time limit: 15 minutes • Peer mark.

• • • • • •

Plenary – Stand Up, Sit Down

What is power of a device measured in?

Watts What is energy normally measured in?

Joules Define a Watt.

1Joule/second How can you calculate Energy?

Energy = Power x Time A light bulb is marked "40W". How much energy will it get through in 10 seconds?

400 Joules How much energy will the same light bulb get through in a minute?

2400 Joules (2.4kJ)