Light is form of energy. It can be used to help us see in the dark, to cut metals ( using a laser ) or to send signals. Light belongs to a group of waves called the electromagnetic spectrum. Visible light is often seen in narrow beams or rays. Light travels in straight lines. This is the reason we ‘see’ shadows as the light cannot bend behind the object. A shadow is an area where the light doesn’t reach.

Lasers produce light of one colour. We can only see laser light when it reflects of something e.g. the dust in the air. Lasers are used in surgery instead of scalpels, to cut metals, to read the information on a bar code and on a DVD.

Light is reflected off shiny objects ( it bounces off them ) We see objects because the sunlight reflects off them into our eyes.

Light travels in straight lines. Light can travel down a fibre optic cable by total internal reflection. The light is reflected off the sides of the cable. A fibre optic cable is a thin thread of glass. Fibre optic cables are used to transmit internet signals, phone conversations and TV signals.

Refraction is the change in speed of light as it travels from one material into another. The light often changes direction. Lens use the process of refraction to change the direction of the light. There are lenses in telescopes, cameras and our eyes.

Convex lenses are used to produce real images ( we can touch them ). These images are upside down ( inverted), smaller than the object ( diminished ) and back to front ( laterally inverted). The lens in your eye acts with the cornea to focus the object onto the retina. Cells on the retina turn the light into electrical energy and send

A concave lens is also called a diverging lens as the rays of light diverge ! Concave lenses are used in some spectacles.

Short sighted people can see close up objects clearly but distant objects are blurred.

Long sighted people can see close up objects clearly but distant objects are blurred.

A rainbow is produced by a similar effect.

Red, green and blue are the primary colours of light. White light is obtained if equal intensities of all three primary colours are mixed. The secondary colours are produced when equal intensities of two primary colours are mixed. Mixing different intensities of the primary colours allows different colours of light to be produced. This is how TV pictures and computer displays are produced.

Ultra violet radiation ( UVR ) is invisible. You should wear suncream to block the UV and sunglasses that absorb it. Exposure to excessive UVR can cause skin cancer. UVR causes you to have a tan but the skin is actually being damaged when you tan.

Ultra violet radiation can also be used to detect forged bank notes. Shining UV light on a bank note causes the security markings to glow ( fluoresce ). Forged bank notes don’t have these security markings. UV can also be used in the treatment of skin disorders. In fact everyone needs to be exposed to UV radiation so that our bodies can produce som essential vitamens.

Infra red Radiation ( IR ) is also invisible. All hot objects give out IR. The police can use this to find criminals in the dark. IR can also be used to transmit signals via a remote control. Doctors can take a thermogram to find parts of the body that are hotter than others. This helps them find cancers.

Heat is a form of energy and can be used to make things happen e.g. to cook food. Heat energy always flows from areas of high temperature to low temperature. When you open your door on a cold winter’s night the energy flows from the house to the outside. Temperature is a measure of how hot or cold an object, it is measured using a thermometer in units of degrees celcius, 0 C.

Heat energy transfers through solids via conduction. The particles in a solid are fixed in position. When heated the particles begin to vibrate more and bump into the particles next to them causing them to vibrate more and causing them to bump into the particles next to them …. Materials that are good conductors are called CONDUCTORS ( metals ). Non metals are called INSULATORS.

Insulators can be used to stop heat energy escaping to the surroundings, they can also be used to keep things cold e.g. fridges have insulating material in the walls.

Heat energy is transferred through liquids and gases via CONVECTION. The particles are free to move, when heated they rise up carrying the heat energy with them. Colder particles fall in to take their place and are in turn heated. Convection currents are responsible for the wind at the seaside.

All hot objects give off INFRA RED RADIATION. This travels in all directions e.g. the food underneath a grill gets cooked via infra red radiation.

Black, dull objects are good absorbers of infra red radiation. White shiny objects are good reflectors of infra red radiation

Shiny, light coloured surfaces are good reflectors of INFRA RED RADIATION.