P1-Topic 2- Electricity 2022

Question 1

State two equations for the power of a circuit. Give

appropriate units. 4

Answer 1

P = I *V    
power = potential difference × current

P = I² R
power = current² × resistance

power, P, in watts, W
potential difference, V, volts, V
current, I, in amperes, A
resistance, R, in ohms, Ω

Question 2

State an equation linking energy transferred, power

and time. Give appropriate units.

Answer 2

E = P*t
Energy (Joules), Power (Watts), Time
(Seconds)

Question 3

State an equation linking energy transferred, power

and time. Give appropriate units.

Answer 3

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

Question 4

What two main factors does the amount of energy

transferred by an appliance depend on?

Answer 4

1. How long the appliance is being used for

2. The power of the appliance

Question 5

Describe the energy transfers in a battery powered torch.

Answer 5

● Battery converts chemical energy into electrical energy

● Bulb converts electrical energy into light as well as waste energy in the form of heating

Question 6

Describe the energy transfers in a battery powered motor.

Answer 6

● Battery converts chemical energy into electrical energy

● Motor converts electrical energy into kinetic energy as well as waste energy
in the form of heating due to friction

Question 7

What three things determine the power of a circuit device?3

Answer 7

1. The potential difference across the circuit
2. The current through the circuit
3. The amount of energy transferred in a given time

Question 8

What is the purpose of the National Grid?

Answer 8

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

Question 9

Where are step-up transformers found in

the National Grid? What do they do? 2

Answer 9

● Step-Up Transformers are used when connecting power stations to transmission cables
● They increase the potential difference

Question 10

Where are step-down transformers found

in the National Grid? What do they do?2

Answer 10

● Step-Down Transformers are used in connecting transmission cables to domestic buildings (like houses)

● They decrease the potential difference

Question 11

Why do transmission lines transfer electricity at high potentials? 3

Answer 11

● 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 12

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

Answer 12

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

Question 13

What can happen when insulating materials are

rubbed together?

Answer 13

They can become (statically) electrically

charged

Question 14

Why can insulators become electrically charged

when rubbed together?

Answer 14

● Electrons are rubbed from one material onto the
other
● The material gaining electrons becomes
negatively charged
● The material losing electrons becomes equally
positively charged