P2 Electricity 4

Question 1

State an equation for the power of a circuit. Give appropriate units.

Answer 1

P = I V

Power ( Watts), Current (Amperes), potential difference (Volts)

Question 2

State an equation linking energy transferred , power and time . Give appropiate unite

Answer 2

E = P t

Energy (joules), Power (watts), Time (seconds)

Question 3

State an equation linking energy transferred , charge flow and potential difference . 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 fork heating

Question 6

Describe the energy transfers in a battery powered torch.

Answer 6

• Battery converts chemical energy into electrical energy
• Bulb converts electrical energy into light as well as waste energy in the form of heating

Question 7

Describe the energy transfers in a battery powered motor.

Answer 7

• 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 8

What three things determine the power of a circuit device ?

Answer 8

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

Question 9

What is the purpose of the National Grid ?

Answer 9

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

Question 10

What are the two types of transformers used in the National Grid?

Answer 10

1. Step-Up Transformers
2. Step-Down Transformers

Question 11

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

Answer 11

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

Question 12

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

Answer 12

• Step-Down transformers are used im transmission cables to domestic buidlings ( like house)
• They decrease the potential difference

Question 13

Why do transmission lines transfer electricity at high potentials ?

Answer 13

• 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 14

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

Answer 14

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