p4: supplying electricity

Question 1

why is the current provided by a cell called a direct current (d.c)

Answer 1

only flows in one direction

Question 2

what is an alternating current

Answer 2

current that repeatedly reverses direction

Question 3

what kind of current is supplied by mains electricity

Answer 3

alternating current

Question 4

what is the frequency and voltage of mains electricity

Answer 4

50Hz, 230V

Question 5

what colors are the live, neutral, and earth wires in a three-core cable

Answer 5

live = brown
neutral = blue
earth = green and yellow striped

Question 6

what is the unction of the live wire in a three-core cable

Answer 6

carries the alternating potential difference from the supply

Question 7

what is the function of the neutral wire in a three-core cable

Answer 7

completes the circuit

Question 8

what is the function of the earth wire in a three-core cable

Answer 8

safety wire to stop the appliance becoming live

Question 9

when is there a current is the earth wire

Answer 9

when there is a fault

Question 10

why is a live wire dangerous

Answer 10

provides a large p.d that would cause a large current to flow through a person if they touched it

Question 11

what is the national grid

Answer 11

national wide network of cables and transformers that link power stations to customers

Question 12

what are step-up transformers used for in the national grid

Answer 12

increase the p.d from the power station to the transmission cables

Question 13

what are step-down transformers used for in the national grid

Answer 13

increase the p.d from the transmission cables to the mains supply in building so it is safe to use

Question 14

what two things does energy transfer to an appliance depend on

Answer 14

power of appliance
time it is switched on for

Question 15

what are the units for
power
current
potential difference
resistance

Answer 15

watts (W)
amps (A)
volts (V)
ohms (Q)