topic 2 - electricity: energy transfers

Question 1

What is the equation which links power, potential difference and current?

Answer 1

power = potential difference x current

Question 2

What is the symbol for power?

Answer 2

P

Question 3

What is the symbol for potential difference?

Answer 3

V

Question 4

What is the symbol for current?

Answer 4

I

Question 5

What is the equation which links power, current and resistance?

Answer 5

power = (current)2 x resistance

Question 6

What is the symbol for resistance?

Answer 6

R

Question 7

What is the power of an appliance?

Answer 7

The amount of energy that it transfers per second.

Question 8

What are the units for power?

Answer 8

watts (W)

Question 9

What are the units for potential difference?

Answer 9

volts (V)

Question 10

What are the units for current?

Answer 10

amps (A)

Question 11

What are the units for resistance?

Answer 11

ohms (Ω)

Question 12

What two factors does the total energy transferred by an appliance depend on?

Answer 12

How long the appliance is on for and it’s power.

Question 13

Will a circuit with high current and potential difference have a high or low power?

Answer 13

High.

Question 14

What are everyday electrical appliances designed to bring about?

Answer 14

Energy transfers.

Question 15

How does a kettle transfer energy from ac mains to the heating device?

Answer 15

Kettles transfer energy electrically from the mains ac supply to the thermal energy store of the heating element inside the kettle.

Question 16

How is energy transferred from the battery of a handheld fan to its electric motor?

Answer 16

Energy is transferred electrically from the battery of a handheld fan to the kinetic energy store of the fan’s motor.

Question 17

What has to flow in a circuit to allow work to be done?

Answer 17

Charge.

Question 18

What is the equation that links energy transferred, power and time (equation for energy transferred by electrical work)?

Answer 18

energy transferred = power x time

Question 19

What is the equation that links energy transferred, charge flow and potential difference?

Answer 19

energy transferred = charge flow x potential difference

Question 20

What is the symbol for energy transferred?

Answer 20

E

Question 21

What is the symbol for power?

Answer 21

P

Question 22

What is the symbol for time?

Answer 22

t

Question 23

What is the symbol for charge flow?

Answer 23

Q

Question 24

What is the symbol for potential difference?

Answer 24

V

Question 25

What are the units for energy transferred?

Answer 25

joules (J)

Question 26

What are the units for power?

Answer 26

watts (W)

Question 27

What are the units for time?

Answer 27

seconds (s)

Question 28

What are the units for charge flow?

Answer 28

coulombs (C)

Question 29

What are the units for potential difference?

Answer 29

volts (V)

Question 30

What is potential difference?

Answer 30

Energy transferred per charge passed.

Question 31

Will a battery with a higher potential difference supply more or less energy to the circuit per coulomb of charge?

Answer 31

More energy.

Question 32

What is the power rating of an appliance?

Answer 32

The maximum safe power that an appliance can operate at.

Question 33

The power rating of an appliance tells you the _______ amount of ______ transferred between stores ___ ______ when the appliance is on.

Answer 33

maximum, energy, per second

Question 34

Why do power ratings help customers choose between models of an appliance?

Answer 34

The lower the power rating, the less electricity an appliance uses in a given time and so the cheaper it is to run.

Question 35

Why does a high power rating not necessarily mean that an appliance transfers more energy usefully?

Answer 35

An appliance may be more powerful than another, but less efficient, meaning that it might transfer the same amount of energy (or less) to the useful stores.

Question 36

What is the National Grid?

Answer 36

A system of cables and transformers linking power stations to consumers.

Question 37

What type of power is transferred from power stations to consumers using the National Grid?

Answer 37

Electrical power.

Question 38

Why do power stations often run well below their maximum output?

Answer 38

So there is spare capacity to cope with an unexpected spike in demand.

Question 39

Why is the National Grid system an efficient way to transfer energy?

Answer 39

It uses a high pd (400,000 V) and a low current which is cheaper and decreases the energy lost by heatint the wires and the surroundings.

Question 40

What is the purpose of step-up transformers in the National Grid?

Answer 40

Increase the potential difference from the power station to the transmission cables.

Question 41

What is the purpose of a step-down transformer in the National Grid?

Answer 41

Decrease, to a much lower value, the potential difference to make the power suitable for domestic use.