OCR Gateway Science - Living for the Future P2

The Sun provides a stable source of heat and light energy. Photocells transfer light into electricity, and glass can provide passive heating for buildings. Wind turbines transfer kinetic energy in the wind into electricity.

Here are some other advantages to photocells:

• no fuel is needed
• no power cables are needed
• they have a long life and are rugged - little maintenance is required

Glass windows provide passive solar heating for buildings. Sunlight passes through the glass and is absorbed by surfaces in the building. It is transferred into heat energy, which is emitted as infrared radiation. This is reflected back into the building by the glass.

Solar collectors use mirrors to focus the Sun’s rays onto a small area. In some parts of the world, this idea is used to make simple solar ovens to cook food without using fuel. More complex solar collectors use curved mirrors to reflect the Sun’s rays onto a focus point. Motors are used so that the collector moves to track the position of the Sun in the sky.

Wind is produced as a result of giant convection currents in the Earth's atmosphere, which are driven by heat energy from the Sun. This means the kinetic energy in wind is a renewable energy resource: so long as the Sun exists, wind will too.

Photocells consist of two types of silicon crystal. When light energy is absorbed by the silicon:

• negatively charged electrons are knocked loose from the silicon atoms
• the electrons flow freely, creating an electric current

The power output of a photocell increases as:

• the light intensity increases
• the exposed surface area increases

Electricity is generated when a coil of wire moves in a magnetic field. This is the basis of electricity generators.

Most electricity is made in power stations by burning fuels. Transformers are used in the National Grid to reduce energy losses from the wires during transmission.

To increase the induced current:

• move the magnet more quickly
• use a stronger magnet
• increase the number of turns on the coil

Batteries produce direct current, or DC, electricity. The current flows in the same direction all of the time. Generators produce alternating current, or AC, electricity. The current reverses direction regularly.

When a wire is moved in a magnetic field, the movement, magnetic field and current are all at right angles to each other. If the wire is moved in the opposite direction, the induced current also moves in the opposite direction.

One side of a coil in a generator moves up during one half-turn, and then down during the next half-turn. This means that, as a coil is rotated in a magnetic field, the induced current reverses direction every half-turn.

Power station -

There are four main stages:

1. the fuel is burned to boil water to make steam
2. the steam makes a turbine spin
3. the spinning turbine turns a generator which produces electricity
4. the electricity goes to the transformers to produce the correct voltage

transformer is an electrical device that changes the voltage…