Electricity

Question 1

What is the unit for current?

Answer 1

Amperes, A

Question 2

What is the unit for voltage?

Answer 2

Volts, V

Question 3

What IS current?

Answer 3

the rate of flow of charge

Question 4

What is the unit for energy?

Answer 4

Joules, J

Question 5

What is the unit for resistance?

Answer 5

Ohms, Ω

Question 6

What IS voltage?

Answer 6

energy transferred per unit charge, joules per coulomb

Question 7

What is the unit for power?

Answer 7

Watts, W

Question 8

What is the equation for charge?

Answer 8

charge = current x time (Q=IT)

Question 9

What is the equation for resistance, voltage and current?

Answer 9

voltage = current x resistance (V=IR)

Question 10

What is the equation for power?

Answer 10

power = current x voltage (P=IV)

Question 11

What is the equation for energy transferred?

Answer 11

energy transferred = power (IV) x time (E=PT)

Question 12

Mains electricity has an…current

Answer 12

alternating current

Question 13

Batteries have a…current

Answer 13

direct current

Question 14

What happens to the current when you increase the resistance?

Answer 14

less current can flow

Question 15

What colour is the neutral wire?

Answer 15

blue

Question 16

What colour is the live wire?

Answer 16

brown

Question 17

What colour is the earth wire?

Answer 17

green and yellow

Question 18

What are the safety features of a plug (the plug itself)?

Answer 18

• right coloured wire connected to each pin - no bare wires showing inside plug - cable grip tightly fastened over the cable outer layer - metal parts made of copper or brass (good conductors) - case, cable grip and cable insulation made of rubber or plastic (good insulators and flexible)

Question 19

Order of wires in a plug?

Answer 19

neutral, earth, live

Question 20

What does the neutral wire do?

Answer 20

current flows out of the neutral wire, which always has 0V

Question 21

What does the live wire do?

Answer 21

current flows in via the live wire, which alternates between a high negative and positive (alternating) voltage of 230V

Question 22

What does the earth wire do?

Answer 22

when there is a fault and the live touches the case, a large current builds up in the live, through the case and is sent down the earth wire.

Question 23

Safety precautions when using plugs?

Answer 23

• damaged (missing/ cracked/ broken case) so that there aren’t exposed live wires which could give you a shock - cable isn’t frayed, exposed live wires - cables aren’t too long, trip hazard - no water near electrics, good conductor - no metal objects in plug as good conductor

Question 24

A plug with metal casing…

Answer 24

must be earthed to an earth wire so that the conductor can never become live

Question 25

A plug with plastic casing...

Answer 25

is double insulated. Plastic is an insulator so stops current flowing. Doesn't need an earth wire.

Question 26

What does a fuse do?

Answer 26

when a fault develops, a surge of current flows though the live and then the earth. This melts the fuse which cuts off the live supply. This isolates the appliance which means you can't get shocked and reduces the fire risk

Question 27

What does a circuit breaker do?

Answer 27

when a circuit breaker detects a surge in current it breaks the circuit by opening a switch

Question 28

What are the advantages of a circuit breaker over a fuse?

Answer 28

- works faster - doesn't have to be replaced, can be reset - works for small current charges which might not melt a fuse but are still dangerous

Question 29

What is an RCCB?

Answer 29

residual current circuit breaker, detects a difference in current between the neutral and the live wire and cuts the circuit

Question 30

What happens when electric current passes through a resistor?

Answer 30

there is a heating effect on the resistor which increases the resistor's resistance, meaning less current can flow.

Question 31

What are the advantages of the heating effect due to a current in a resistor?

Answer 31

- melts fuses - can be used in toasters to cook bread

Question 32

What IS power?

Answer 32

the rate of energy transfer

Question 33

What do you need to know to work out a fuse rating?

Answer 33

current

Question 34

An ammeter must be placed in...

Answer 34

series

Question 35

A voltmeter must be placed in...

Answer 35

parallel

Question 36

the gradient of an I-V graph is...

Answer 36

1/Resistance

Question 37

Metal filament lamp I-V graph

Answer 37

as temperature increases, resistance increases, hence curve.

Question 38

Wire I-V graph

Answer 38

current at a contant temp is proportional to voltage

Question 39

Diode I-V graph

Answer 39

current will only flow in one direction

Question 40

Different resistors I-V graph

Answer 40

current through a resistor at a constant temp is proportional to voltage. Different resistors have different resistances, hence slope.