Electricity- domestic uses and safety

Question 1

Equation for power

Answer 1

P = I X V
- p is in watts
- I is in amps
- V is in volts

Question 2

Equation for power (yes there is another one)

Answer 2

P = I^2 x R
- P is in watts
- I is in amps
- R is in ohms

Question 3

Equation for energy transferred

Answer 3

E = P X T
- E is in joules
- P is in watts
- T is in seconds

Question 4

Eqation for energy tranferred (the other one)

Answer 4

E = Q X V
- E is in joules
- Q is in coulombs
- V is in volts

Question 5

Equation for voltage

Answer 5

V = I X R
- V is in volts
- I is in amps
- R is in ohms

Question 6

What is a direct current

Answer 6

• provided by a direct pd. (constnat value)
• current always flows in the same direction in the circuit
• d.c. source is battery

Question 7

What is alternating current

Answer 7

• provided by alternating pd. (size is always changing and keeps changing direction)
• mains supply is a a.c. source

Question 8

What is the frequency of the mains supply and how many v is it

Answer 8

50 hertz
230 volts

Question 9

What does the earth wire do and what colour is it

Answer 9

• green and yellow
• protects the user from an electric shock, sends the current to ground instead

Question 10

What does the neutral wire do and what colour is it

Answer 10

• blue
• completes the circuit

Question 11

What does the live wire do and what colour is it

Answer 11

• brown
• carries the current (dangerous wire)

Question 12

What is the function of a fuse

Answer 12

• stops overheating
• protects against fires that could be caused from too much current flowing

Question 13

what is the function of a cable grip?

Answer 13

• holds the cable firmly in place so that the wires don’t get pulled from their connections

Question 14

what is double insulation?

Answer 14

• outer case of the appliance is plastic (as well as the plug)
• eliminates the need for an earth wire as you won’t get a shock from toucing a plastic wire

Question 15

what is the national grid

Answer 15

system of cables and transformers linking power stations to consumers
- electrical power is transferred from the power stations to the consumers using the National Grid
- step-up transformers are used to increase the p.d. from the power station to the transmission cables high pd, low current as the wires get too hot and will more energy will be wasted due to higher resistance
- step-down transformers are used to decrease to a much lower value, the pd. for domestic use.