Power and Efficiency

How can you find the power of an appliance?

• see how hot it gets when switched on

• see what voltage it needs

• look for the efficiency label

• look for the power rating on the label

How do we calculate percentage efficiency?

• (useful energy out ÷ total energy in) × 100

• (useful energy in ÷ total energy out) x 100

• (total energy out ÷ useful energy in) x 100

Calculate the efficiency of a bulb with an input energy of 50J, which outputs 40J of thermal energy and 10J of light energy.

• 10%

• 20%

• 25%

• 50%

Which kinds of appliances transfer the most energy?

• heaters and cookers

• lights

• TVs and radios

• computers

Tags

NGSS.MS-PS3-3

NGSS.MS-PS3-4

What is missing from this formula to calculate efficiency of an appliance?

• x 100

• + 100

• - 100

• / 100

Tags

NGSS.MS-PS3-4

NGSS.MS-PS3-5

What is the definition of Power?

• The rate at which energy is used

• How much heat energy is released

• How strong a person is

• How long you leave the lights on for

What are the units for measuring Power?

• W

• J

• kg

• mL

How much is 1 W?

• 1 J per second

• 10 J per second

• 1 J per minute

• 10 J per minute

How much electrical energy does a 20 W electric light use every second to stay lit?

• 20 J

• 200 J

• 1 J

• 10 J

What is the useful energy output for a hairdryer that has an input energy of 9J and waste output energy of 5J?

• 4J

• 14J

• 45J

• 9J