Ch5 Electricity in the home

Question 1

UK mains electricity

Answer 1

AC supply
frequency of 50Hz
pd of 230V

Question 2

Alternating current

Answer 2

Flows one way then the opposite way in successive cycles

Question 3

Direct current

Answer 3

flows only in one direction

Question 4

Power

Answer 4

P=IV
= I^2R
= V^2/R

Question 5

Electrical energy

Answer 5

QV
VIt
Pt

Question 6

National grid

Answer 6

nationwide network of cables and transformers

supplies electrical power from power stations to homes and buildings

Question 7

Step-up transformers

Answer 7

used to increase the potential difference
from the power station to the transmission cables

increases efficiency

• much less current needed to transfer same amount of power
• power loss due to resistance heating in cables is reduced

Question 8

Step-down transformers

Answer 8

used to decrease, to a much lower value, the

potential difference for domestic use

Question 9

efficiency

Answer 9

useful output/total input