Efficiency

Question 1

A bulb transfers 200J of electrical energy into 150 joules of light energy. What happened to the other 50J?

Answer 1

It transferred to another energy store, e.g heat.

Question 2

What is waste energy?

Answer 2

Extra energy that is not needed, e.g. heat produced from a light.

Question 3

What does the conservation of energy mean?

Answer 3

Energy cannot be created or destroyed. Energy can only be transferred from one store to another.

Question 4

How do you calculate efficiency?

Answer 4

Useful energy out/total energy in x100% or useful power out/total power in x100%

Question 5

An engine has an efficiency of 35%. It transfers 50J of useful energy. How much energy was put in?

Answer 5

K - Efficiency=0.35, useful out=50J, total in=?
E - Efficiency=useful out/total in
W - 0.35=50/total in, total in=50/0.35=143
U - 143J

Question 6

If energy is wasted by friction, what can improve efficiency?

Answer 6

Using a lubricant

Question 7

If energy is wasted through a wall, what can improve the efficiency?

Answer 7

Thermal insulation