# Physics note P1A part 2

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• Created by: ok
• Created on: 25-05-11 18:13

POWER = CURRENT X VOLTAGE

EFFICIENCY = USEFUL OUT PUT / TOTAL INPUT X 100%

ENERGY TRANSFERRED (kWh or units) =POWER(kW) X TIME(h)

TOTAL COST= POWER(kW) X TIME(H) X COST OF ONE kWh

PAY BACK TIME = COST/SAVING

Wind power

• Will work as long as the wind is blowing
• Requires low maintenance
• Energy is free as long as the wind is blowing
•

• The wind is not very reliable
• Does not look attractive
• Noise causes disturbance to the local neighbours

Solar energy (Photo voltaic cells flows in direct current)

• Energy is free
• Reliable in sunny areas as long as the sun is shining energy can be made
• Heat water without using any electrical equipment
• Can work on cloudy days

• Expensive to put together

Motors
Motors are used in every day electrical applicances, the three things needed in a motor is some wire, a magnet and an electrical current
If you pass a wire through a magnet then a magnetic field is created.If this field is permanent then the wire will move, if you hold the wire still then the magnet will move. This is called the motor effect. Electrical motors also turn electrical energy into kinetic energy
This summarizes how a motor works

• Inside a magnetic field a coil of wire is wrapped around a magnet (core)
• The wire can spin on the axis and is free from being tangled
• The current always flows in the same direction so that the motor spins in the same direction
• The current passes through the coil and makes it magnetic, this interacts with the permanent magnet and spins it

The national grid
The National Grid is a network of pylons and cables