# The National Grid

Electricity is transferred from the power station to consumers along the national grid. The power lines across the country connect together all the power stations with all the people who want to use electricity.

• electricity can be used from any power station to meet demand in any part of the country.
• power stations can be built away from large cities and near the natural resources that they need to use.
• any extra electricity in the system can be used to pump water up hill to be used later to generate electricity in a hydroelectric  power station.
• if a power station needs to be turned off for any reason the consumers (houses and businesses) can continue to receive electricity from other power stations.

Electrical Power

If we know the potential difference across an electrical component and the current flowing through it we can calculate the electrical power. Power is measured in watts (W).  A power of 60 W means that 60 joules of energy are being delivered every second.

power         =         potential difference     x        current

(watts, W)                     (volts, V)                         (amps, A)

Example; What is the power dissipated by a resistor of 0.5 A of current flow through it when 12 V of potential difference are applied to it?

Step-up & Step-down transformers

Step-up transformers –  step up (increase) the potential difference.

Step-down transformers – step down (decrease) the potential difference.