ENERGY AND EFFICIENCY

Question 1

what is the input energy?

Answer 1

the energy supplied to the device

Question 2

what is the useful output energy?

Answer 2

the useful energy transferred by the device

Question 3

what is weight measured in?

Answer 3

newtons (N)

-the weight of a 1 kg object on the Earth’s surface is about 10N

Question 4

friction between the moving parts causes heating=

Answer 4

lubricate the moving parts to reduce friction

Question 5

the resistance of a wire causes the wire to get hot when a current passes through it

Answer 5

in circuits, wires with as little electrical resistance as possible are used

Question 6

air resistance causes a force on a moving object that opposes its motion. Energy transferred from the object to the surroundings by this force is wasted.

Answer 6

streamline the shapes of moving objects to reduce air resistance

Question 7

sound created by machinery causes energy transfer to the surroundings

Answer 7

cut out noise (tighten loose parts to reduce vibrations)

Question 8

efficiency =

Answer 8

useful output energy transferred by the device (J) / total input energy supplied to the device (J)

Question 9

can a device be more than 100% effective?

Answer 9

no as you can never get more energy from a machine than you put into it

Question 10

investigating efficiency

Answer 10

• use an electric winch to raise a weight
• use the joulemeter to measure the energy supplied
• calculate the change in the gravitational potential energy store of the weight
• make some measurements to find out whether lubricating the axle of the electric motor with a few drops of suitable oil makes the winch more efficient
• switch the motor off when lubricating

safety: protect the floor and your feet and stop the winch before the masses wrap round the pullery

Question 11

why are electric heaters usually 100% efficient?

Answer 11

all of the electrostatic energy is transferred to the “useful” thermal energy store