magnetism - transformer calculations

Question 1

when can you work out potential difference of secondary coil?

Answer 1

if we know the p.d of primary coil and the number of coils in primary + secondary coil

Question 2

Vp Np
— = —
Vs Ns

Answer 2

potential difference (primary) number of turns (primary)
—————————————— = ——————————————
potential difference (secondary) number of turns (secondary)

Question 3

what must happen to power in transformers?

Answer 3

be conserved

Question 4

power of primary coil =

Answer 4

power of secondary coil

Question 5

how do work out power of a transformer?

Answer 5

VpIp = VsIs
potential difference (p) x current (p) = potential difference (s) x current (s)

(only applies if 100% efficient which we assume happens in calculations but in practice it is not)

Question 6

how is power transmitted and what is the problem?

Answer 6

electrical power transmitted from power stations to homes through high voltage cables. when transmitting large amount of power, we either use large current or a large voltage. problem is that power is wasted in transmission cables as heat. amount of waste as heat depends of square of the current.
large current in transmission cables = huge amount of power wasted as heat. so instead of large current, we use large p.d

Question 7

how to solve energy waste in transmission cables?

Answer 7

use a large p.d. the electricity from the power stations to is first passed through a step up transformer. this steps up p.d to around 400,000 V. electrical power transmitted down high voltage cables and then passed through step down transformers. these reduce p.d. (p.d of mains supply in UK is 230 V)

Question 8

advantage of transformers

Answer 8

reduce power wastage in national grid