Efficiency

Question 1

What is the second principle of conservation of energy that you need to know?

Answer 1

Energy is only useful when it is transferred from one store to a useful store.

Question 2

What does ‘dissipated’ mean?

Answer 2

Saying that the energy is spread out, and so is ‘lost’.

Question 3

Why is some of the input energy always dissipated or wasted?

Answer 3

• Whenever work is done mechanically, frictional forces have to be overcome, including things like moving parts rubbing together, and air resistance.
• The energy needed to overcome these frictional forces is transferred to the thermal energy stores of whatever’s doing the work and the surroundings.

Question 4

What is the equation for the conservation of energy principle?

Answer 4

total energy input = useful energy output + wasted energy

Question 5

What must there be LESS of to make a device MORE efficient?

Answer 5

The less wasted energy there is, the more efficient the device is.

Question 6

What is the equation for efficiency?

Answer 6

Efficiency = useful energy transferred by device (J) ÷ total energy supplied to device (J)

Question 7

Why can the efficiency of a device never be 100%?

Answer 7

All devices have efficiency, but because some energy is ALWAYS wasted, the efficiency can never be equal to or higher than 1 (or 100%).