P7

Question 1

What is energy?

Answer 1

Quantity that tells you what is possible but not what will happen

Question 2

What are the 8 different stores of energy and their equations?

Answer 2

Chemical - no equation, glucose in our muscles with oxygen
Thermal - m x temperature difference
Kinetic - 0.5 x m x v^2
Gravitational - mgh
Elastic - 0.5 x k x e^2
Nuclear - change in mass x speed of light ^2
Electrostatic - none
Magnetic - none

Question 3

What are the different ways energy can be transferred?

Answer 3

Mechanically (with forces)
Electrically (with an electric current)
Heating by particles
Heating by radiation

Question 4

What are the equations for transferring energy mechanically and electrically?

Answer 4

Mechanically: work done = force x distance
Electrically: energy transferred = electrical power x time

Question 5

What is the law of conservation?

Answer 5

Energy cannot be created or destroyed
Only transferred between stores

Question 6

How can you analyse a situation using energy?

Answer 6

1) choose two points
2) identify which stored have more or less energy in them at those points
3) work out which type of transfer has transferred the energy between stores

Question 7

How do you work out the energy in different situations?

Answer 7

DO QUESTIONS
PMT

Question 8

How is energy transferred in electric devices?

Answer 8

From a chemical store of a battery
OR
From a chemical or nuclear store of the fuel in a power station used to produce mains electricity

Question 9

What does the power rating tell us?

Answer 9

Rate at which the appliance transfers energy between stores
Large power rating means the appliance will transfer more energy per second do the battery runs out faster

Question 10

How do you work out power?

Answer 10

PET
power = (electrical) work done/time

Question 11

What does an electrical appliances do?

Answer 11

Transfers energy electrically from chemical stores

Question 12

What do electrical devices do?

Answer 12

Changes electrical transfer to other forms of energy transfer to do a particular job

Question 13

How do different appliances transfer energy between stores?

Answer 13

TV - runs off mains, chemical to thermal store
DVD player - runs off mains, chemical to kinetic
Smartphone - runs off a battery, chemical to thermal store

Question 14

How can you increase the energy in a thermal store?

Answer 14

• burning a fuel
• using an electric current to transfer energy form a fuel

Question 15

What is energy dissipation?

Answer 15

When the energy or radiation transferred has been absorbed by the surroundings which heats them up

Question 16

What is lubrication?

Answer 16

Reducing the energy dissipated due to friction (using oil)

Question 17

What is insulation?

Answer 17

Reducing the energy dissipated due to heating

Question 18

How does oil cause lubrication?

Answer 18

Oil creates a layer of fluid between two solid surfaces
The surfaces are no longer in direct contact and friction is reduced
Important in car engines

Question 19

What is efficiency?

Answer 19

Tells us how good the appliance is at doing its job and is expressed as a ration or percentage
No appliance can be 100% efficient as energy is always dissipated

Question 20

What is the equation for efficiency?

Answer 20

Efficiency (%) = useful output energy transfer/input energy transfer

Question 21

What is the Sankey diagram?

Answer 21

Illustrates the efficiency
The width of the arrow shows the amount of energy transferred

Question 22

How can we increase efficiency?

Answer 22

• use insulation to reduce heating of the surroundings
• make devices from materials that reduce unwanted energy transfer
• use technology to produce devices that are better at their job