5.10 Energy and Power

Energy (E)the ability to do workMeasured in Joules (J)

Power (P)the amount of work that can be

accomplished in a certain amount of timeMeasured in Watts (W)

Energy

the ability to do workall appliances need energy to work ex. a hair dryer needs to be plugged

in to get energy to work ex. a remote control needs energy

from batteries to work

What is energy?

Power

the rate at which energy is used or the amount of work done per second

Is measured in WattsA microwave that uses more Watts

will heat food faster!

What is power?

Symbols and Units

Symbol =

Units =

Symbol =

Units =

Power

Watts (W)

Energy

Joules (J)

Time

Seconds (s)

E = P x Δt

A stereo has a power rating of 200W & is used for 1800 seconds. How much energy is used?

E = P x Δt = 200 x 1800E = 360 000J

A video game has a power rating of 175W & is used for 3600 seconds. How much energy is used?

E = 630,000 J 630,000 Joules of energy were used to work the video game

E = P x Δt

= 175 x 3600

A hair dryer has a power rating of 425W & is used for 10 minutes. How much energy is used?

E = 255,000 J 255,000 Joules of energy were used to work the hair dryer

Time must be in seconds

10 min x 60 = 600 seconds

E = P x Δt

= 425 x 600

How do we pay for the energy we use?

Energy can also be measured in kilowatt hours (kWh). If we use 1000W in 1 hour, we consume

1 kWh = 3 600 000 J

KWh is used by Hydro Quebec to calculate your energy bill

For a average summer day. Mrs “I” uses 44 kWhs. 30 kWh x $0.0532 = $1.596 14 kWh x $0.0751 = $1.051

$2.647

This is just for ONE day.

P = IV

Power

Watts (W)Current

Amps (A)

Voltage

Volts (V)

A toaster requires 120V & 6A to work. What is its power?

P = I•V

P = (6)•(120)

P = 720 W

The toaster has 720 watts of power

An appliance requires 240V & 2A to work. What is its power?

P = I•V

P = (2)•(240)

P = 480 W

The appliance has a power of 480 watts

An appliance requires 120V & 12A to work. It is used for 900 seconds. How much energy is used?

Tricky Question

An appliance requires 120V & 12A to work. It is used for 900 seconds. How much energy is used?

P = I•V

P = (12)•(120)

P = 1440 W

Tricky Question

E =1,296,000 J

E = P x Δt

= 1440 x 900

An appliance uses 225V & 4A to work. It is used for 1 hour. How much energy is used?

P = I•V

P = (4)•(225)

P = 900 W

Tricky Question

E =3,240,000 J

60min x 60

E = P x Δt

= 900 x 3600