Efficiency of Machines

Question 1

What is efficiency the measure of?

Answer 1

How much energy is usefully transferred

Question 2

What is the input energy of an electrical device e.g. a television?

What are it’s output energies?

Answer 2

Electrical energy

1. Sound energy
2. light energy
3. thermal energy

Question 3

What is the input energy of a battery?

What are it’s output energies?

Answer 3

Chemical energy

1. Electrical energy
2. Thermal energy

Question 4

What is the input energy of electrical generation e.g. wind turbines?

What are it’s output energies?

Answer 4

Kinetic energy

1. Electrical energy
2. Thermal energy

Question 5

What is the input energy of potential energy e.g. firing a bow and arrow?

What are it’s output energies?

Answer 5

Elastic potential energy

1. Kinetic energy
2. Thermal energy

Question 6

Most energy transfers involve some ____, often as ____ ____

Answer 6

Most energy transfers involve some losses, often as thermal energy

Question 7

The less energy is ‘wasted’, the more ____ a device is said to be

Answer 7

The less energy is ‘wasted’, the more efficicent a device is said to be

Question 8

Define a ‘macine’

Answer 8

A machine is a device which turns one type of energy into another

Question 9

What is the formula for energy efficiency?

Answer 9

Efficiency = Useful energy out / Total energy in

Question 10

What is the formula for power efficiency?

Answer 10

Efficiency = Useful power out / Total power in

(exactly the same as energy efficiency)

Question 11

What 2 ways can you give efficiency in the form of?

Answer 11

1. A decimal
2. A percentage

Question 12

What are the formula triangles for energy and power efficiency?

Answer 12

Question 13

Is any device 100% efficient?

Answer 13

No - not usually

Question 14

What is wasted energy usually spread out as?

Answer 14

Thermal energy (heat)

Question 15

What is the exception to no device being 100% effecient?

Answer 15

Electric heaters - all the electricity is converted into thermal energy (‘useful’ energy)

Question 16

What, ultimately all energy end up as?

Answer 16

Thermal energy

Question 17

If you use an electric drill, you get ____ ____ of energy, but they all quickly end up as ____ ____

Answer 17

If you use an electric drill, you get various types of energy, but they all quickly end up as thermal energy

Question 18

What is useful energy?

Answer 18

Concentrated energy

Question 19

How does thermal energy make the energy less concentrated?

Answer 19

The thermal energy is transferred to the cooler surroundings, which then beome warmer. As the thermal energy is transferred to cooler surroundings, the energy becomes less concentrated - it dissipates

The total amount of energy stays the s​ame. The energy is still there, but as it becomes increasingly spread out, it can’t easily be used or collected back in again

Question 21

When a questions asks ‘why is the input energy more than the (useful) output energy’, what do you answer?

Answer 21

Because some energy is wasted as heat