Electricity

Question 1

What is electric current?

Answer 1

The flow of electrical charge.

Question 2

State the equation linking charge, current, and time

Answer 2

Charge = Current x Time

Question 3

What can be said about the value of current at any point in a single closed loop?

Answer 3

The current is the same at all points in a closed loop.

Question 4

What two factors does the current in a circuit depend on?

Answer 4

Potential Difference (V)
Resistance (R)

Question 5

What is the potential difference (voltage)?

Answer 5

It is a measure of the difference in electrical energy between two parts of a circuit

Question 6

What equation should be used to calculate the potential difference?

Answer 6

Potential Difference = Current x Resistance (Ω)

Question 7

What is an ‘Ohmic Conductor’?

Answer 7

A conductor for which current and potential difference are directly proportional
Resistance remains constant as current changes
Temperature must be constant

Question 8

What happens to the resistance of a filament lamp as the temperature increases? Why?

Answer 8

Resistance increases
Ions in metal have more energy, so vibrate
more, causing more collisions with electrons as they flow through the metal, creating greater resistance to current flow

Question 9

Give two examples of when a thermistor may be used.

Answer 9

In a thermostat to turn a heater on below a certain temperature
In a freezer turn on a cooler when the temperature becomes too high

Question 10

State what happens to the resistance of an LDR as light intensity decreases.

Answer 10

LDR’s resistance increases

Question 11

How does the potential difference across two components vary when connected in series and parallel?

Answer 11

Series: Total P.D is shared between each component

Parallel: P.D across each component
is the same

Question 12

Describe the current in a series circuit.

Answer 12

The current is the same at all positions since the charge only has one path to flow through.

Question 13

Describe the current in a parallel circuit.

Answer 13

The current is shared between the different branches. When the charge reaches a junction it splits.

Question 14

How should you connect an ammeter in a circuit to measure current?

Answer 14

Ammeters should be connected in series with the component that they are measuring current through.

Question 15

How should you connect a voltmeter in a circuit to measure potential difference?

Answer 15

Voltmeters should be connected in parallel to the component that they are measuring the potential difference of.

Question 16

State two equations for the power of a circuit.

Answer 16

P = I V
P = I^2 R

Question 17

State an equation linking energy transferred, power and time.

Answer 17

E = Pt
Energy (Joules), Power (Watts), Time (Seconds)

Question 18

State an equation linking energy transferred, power and time.

Answer 18

E= Q V
Energy (Joules), Charge (Coulombs), Potential Difference (Volts)

Question 19

What is the purpose of the National Grid?

Answer 19

To link power stations to consumers so that they have access to a source of electricity.

Question 20

Where are step-up transformers found in the National Grid? What do they do?

Answer 20

Step-up transformers are used when connecting power stations to
transmission cables
They increase the potential difference

Question 21

Where are step-down transformers found in the National Grid? What do they do?

Answer 21

Step-down transformers are used in connecting transmission cables to
domestic buildings (like houses)
They decrease the potential difference

Question 22

Why do transmission lines transfer electricity at high potentials?

Answer 22

A high potential, results in a low current
The lower the current, the less energy that is wasted as heat
Therefore it is more efficient

Question 23

Why does the potential need to be decreased between transmission lines and houses?

Answer 23

Lower potentials are safer for domestic use and reduce the likelihood of
severe electrocution
Appliances are designed for 230V

Question 24

What supply does the mains electricity use?

Answer 24

A.C (alternating current)

Question 25

What is alternating current

Answer 25

Current that continuously changes direction at a
specific frequency

Question 26

What is direct current

Answer 26

Current that only flows in one direction.

Question 27

What is the UK’s frequency?

Answer 27

50Hz

Question 28

What is the UK’s volatage?

Answer 28

230V

Question 29

How many wires are usually in the cables connecting electrical appliances to the mains? Name these wires

Answer 29

1. Live wire
2. Neutral wire
3. Earth wire

Question 30

State the insulation colour used on the Earth wire

Answer 30

Green and Yellow Stripes

Question 31

State the insulation colour used on the live wire

Answer 31

Brown

Question 32

State the insulation colour used on the Earth wire

Answer 32

Blue

Question 33

Explain when the Earth wire does and doesn’t carry a current

Answer 33

Under normal circumstances, no current flows through the Earth wire
If a fault occurs in the appliance (such as a surge or the causing becoming live), current will flow to the ground

Question 34

What is the purpose of the neutral wire?

Answer 34

To complete the circuit by connecting the appliance back to the mains supply

Question 35

For metal appliances, where is the Earth wire connected to? Why?

Answer 35

Earth wire is connected to the metal casing of the appliance
If live wire becomes loose and touches the casing, the current will flow through the Earth wire, preventing electrocution