Topic 2: Electricity

Question 1

What are the three wires in a plug?

Answer 1

live, neutral, earth

Question 2

What voltage is the neutral wire?

Answer 2

0V

Question 3

What is the purpose of an earth wire?

Answer 3

for safety - reduce danger of electric shock

Question 4

Why are wires covered in plastic casing?

Answer 4

plastic acts as an insulator so prevents you from getting an electric shock

Question 5

How does a fuse work?

Answer 5

if there is a big surge in current, the fuse ‘blows’ (melts) which cuts off the live supply

Question 6

Why do we need a fuse?

Answer 6

it isolated the appliance and makes an electric shock impossible and prevents risk of fire

Question 7

What wire in a plug is connected to the fuse?

Answer 7

live wire

Question 8

What are the advantages of a circuit breaker?

Answer 8

-they can be easily reset
-much faster than fuses (safer)
-can detect smaller current changes

Question 9

What is the difference between AC and DC current?

Answer 9

AC: mains electricity, current constantly changing direction
DC: batteries and cells, current always in same direction

Question 10

What happens when an electric current is in a resistor?

Answer 10

energy transfer - heats up the resistor

Question 11

Why does a resistor heat up?

Answer 11

electrons collide with the ions that make up the resistor - giving the ions more energy

Question 12

How does heating effect a resistor?

Answer 12

increases the resistance - less current will flow

Question 13

How does heating effect a circuit?

Answer 13

components melt - circuit will stop working

Question 14

What is current?

Answer 14

rate of flow of charge

Question 15

Current is proportional to…

Answer 15

voltage

Question 16

(resistance) As the temperature of a metal filament increases….

Answer 16

resistance increases

Question 17

Current will only flow through a diode in one…

Answer 17

direction

Question 18

What does I stand for in Q=It?

Answer 18

current

Question 19

What does Q stand for in Q=It?

Answer 19

charge

Question 20

Voltage, current and resistance equation

Answer 20

Voltage = current x resistance

Question 21

The steeper a voltage/ current graph the…

Answer 21

lower the resistance

Question 22

If the voltage/ current graph shows a curve, it means that…

Answer 22

the resistance is changing

Question 23

LDR: in bright light the resistance…

Answer 23

decreases

Question 24

LDR: in dark light the resistance….

Answer 24

increases

Question 25

What is a use of an LDR?

Answer 25

burglar detectors

Question 26

Thermistor: in hot conditions the resistance…

Answer 26

decreases

Question 27

Thermistor: in cold conditions the resistance…

Answer 27

increases

Question 28

What is a use of a thermistor?

Answer 28

car engine temperature detector sensors

Question 29

Why are light-emitting diodes useful?

Answer 29

emit light when current flows through them in the forward direction

Question 30

What are 2 uses of light-emitting diodes?

Answer 30

-traffic lights
-remote controls

Question 31

What is the total resistance in a series circuit?

Answer 31

total resistance of resistance of each component in the circuit

Question 32

Why does a resistor heat up?

Answer 32

electrons collide with the ions in the resistor lattice - releasing energy

Question 32

Example of an appliance with high resistance

Answer 32

toaster - coils of wire give off infrared radiation

Question 32

What is electrical power?

Answer 32

the rate at which an appliance transfers energy

Question 33

What is power measured in?

Answer 33

Watts (W)

Question 34

Electrical power, current and voltage equation

Answer 34

power = current x voltage

Question 35

What should fuses current ratings be?

Answer 35

just higher than the operating current

Question 36

Energy, current, voltage and time equation

Answer 36

energy = current x voltage x time

Question 37

Charge, current and time equation

Answer 37

charge = current x time

Question 38

When charge goes through a change in voltage, then…

Answer 38

energy is transferred

Question 39

The bigger the change in voltage, the more…

Answer 39

energy is transferred

Question 40

A battery with a bigger voltage will provide more…

Answer 40

energy for the circuit

Question 41

What is voltage?

Answer 41

the energy transferred per unit charge passed

Question 42

One volt =

Answer 42

one joule per coulomb

Question 43

Energy transferred, voltage and charge equation

Answer 43

energy = charge x voltage

Question 44

Energy transferred, charge, current and resistance equation

Answer 44

energy = charge x current x resistance

Question 45

How does a photocopier work using electrostatics?

Answer 45

-image plate/drum is positively charged
-white paper reflects light making the white areas of the drum leak away
-negatively charged toner is attracted to the positively charged image

Question 46

How does an inkjet printer work using electrostatics?

Answer 46

-ink negative charge
-two metal plates surrounding ink are oppositely charged
-ink repels from negative plate onto positive plate

Question 47

How does lightning form?

Answer 47

-air particles rub against each other
-charge build up in clouds
-build up discharges between the ground and the cloud
-stream of electrons which can cause fires

Question 48

How does an aircraft become electrically charged?

Answer 48

-air rubbing against aircraft (friciton)
-can cause a spark

Question 49

What is double insulation?

Answer 49

appliance made of plastic casing