T2 energy transfers

Question 1

state 2 equations for the power of a circuit

Answer 1

P = I V P = I² R

power (watts), current (amperes), potential difference (volts), resistance (ohms)

Question 2

equation linking energy transferred, power and time

Answer 2

E = P t

energy (joules), power (watts), time (seconds)

Question 3

equation linking energy transferred, charge flow and potential difference

Answer 3

E = Q V

energy (joules), charge (coulombs), potential difference (volts)

Question 4

what 2 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 coverts 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 3 things determine the power of a circuit device

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

2 types of transformers used in the National Grid

Answer 9

1. step-up transformers

2. step-down transformers

Question 10

where are step-up transformers found in the National Grid

what do they do

Answer 10

• used when connecting power stations to transmission cables

- increase the potential difference

Question 11

where are step-down transformers found in the National Grid

what do they do

Answer 11

• used in connecting transmission cables to domestic buildings (like houses)
• decrease the potential difference

Question 12

why do transmission lines transfer electricity at high potentials

Answer 12

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

Question 13

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

Answer 13

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