Electricity

Question 1

Define current.

Answer 1

The flow of electrical charge.

Question 2

State the equation that links current, charge and time.

Answer 2

charge flow = current / time

Question 3

What is meant by the potential difference in a circuit?

Answer 3

PD (voltage) is what “pushes” the charge around the circuit.

Question 4

What is the equation that links potential difference, current and resistance?

Answer 4

PD = current x resistance

Question 5

True or false? The resistance of an LDR increases with light intensity.

Answer 5

False

Question 6

What happens to the resistance of a thermistor as it gets hotter?

Answer 6

The resistance decreases.

Question 7

True or false? Potential difference is shared between components in a series circuit.

Answer 7

True

Question 8

How does the current through each component vary in a series circuit?

Answer 8

Current is the same in all components.

Question 9

True or false? Current is shared between the branches of a parallel circuit.

Answer 9

True

Question 10

A resistor is in series with a cell. A second resistor is added in parallel to the first. How does the overall resistance of the circuit change?

Answer 10

The overall resistance is reduced.

Question 11

True or false? Mains supply electricity is an alternating current.

Answer 11

True

Question 12

What is the potential difference and the frequency of the UK mains supply?

Answer 12

PD - 230V

Current - 50Hz

Question 13

Name and give the colours if the three wires in a three-cord cable.

Answer 13

Neutral wire - blue
Live wire - brown
Earth wire - green and yellow

Question 14

Explain why touching a live wire is dangerous.

Answer 14

A large potential difference is produced and a current flows through you.

Question 15

Describe the energy transfers that occur for a battery powered fan.

Answer 15

Energy is transferred electrically from the battery to the kinetic energy store in the motor.

Question 16

What is the power rating of an appliance?

Answer 16

The maximum safe power that it can operate at.

Question 17

State three equations that can be used to calculate electrical power.

Answer 17

d

Question 18

What is the national grid?

Answer 18

A giant web of wires that delivers electricity to buildings/homes from power stations.

Question 19

Explain why electricity is transferred by the national grid at a high pd but low current.

Answer 19

It is much cheaper to boost the PD really high and keep the the current as low as possible.

Question 20

What are the functions of step-up and step-down transformers?

Answer 20

Step up transformers increase potential difference.

Step down transformers decrease potential difference.