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The nature of light. Light and Colours. What is light ? The electromagnetic spectrum Light of the Sun The nature of light Laser Colours. What is light ?. Light may be considered as waves or particles – that depends on the type of investigation. The particles of light are called photons.

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the nature of light

The nature of light

Light and Colours

slide2
What is light ?
  • The electromagnetic spectrum
  • Light of the Sun
  • The nature of light
  • Laser
  • Colours
what is light

What is light ?

Light may be considered as waves or particles – that depends on the type of investigation. The particles of light are called photons.

For most purposes the light may be described as electromagnetic waves. I.e. the light is related to radio waves, microwaves and thermal radiation = infrared light, but these waves all have a wavelength that is longer than the visible light. This also means that they have a lower energy but of course you have to pay attention to microwave ovens and heaters, due to the intensity.

The electromagnetic waves, with a wavelength shorter than visible light, include ultra violet-light (UV), X-rays and gamma rays. These waves hold much energy and are dangerous in high quantities.

slide5

An electromagnetic wave has both an electric field (E) and a magnetic field (B). They are at right angles to each other. You can change the frequency f and the wavelength λ. The speed of light c = λ • f.

light of the sun

The white light of the Sun contains a spectrum of colours which become visible when looking at it through a prism. The wavelength of the colours differs and is therefore refracted into various angles .

The velocity of light in space is 300,000 km per second. That means that the light of the Moon takes 1 second to reach the Earth.

Light of the Sun

It takes 8 minutes for the light to reach the Earth

the nature of light 1

The wavelength of light determines our perception of the colour of the light. Light with a short wavelength we perceive as violet or blue colours while light with a long wavelength is reddish. Green and yellow light have wavelengths between blue and red light.

The nature of light 1

The wavelength λ is measured in nanometres (nm) as 0,000000001 metre. The number of wave movements of the light per second is the frequency of light and is measured in hertz (Hz). The wavelength of the light and the frequency of the light are connected, as the velocity of light is c = λ • f

the nature of light 2

The light spreads in straight lines until it hits something that can change its orbit or absorb it. These lines are called rays of light.

The light can be absorbed by a lightproof material as for example a human being in sunlight. The shadow is where the sun is lacking.

The nature of light 2

Light can be deflected or refracted for example when a ray of light goes through air and hits water. The light then continues into the water and the ray of light is refracted. At last it takes another direction. The same happens when light hits glass for example a window or a prism of glass.

Light can be reflected – that is why we are able to look at ourselves in a mirror

slide9

Snell´s law – the law of refraction explains how light is changing direction from one material to another. The fish is not where it seems to be. You may move the fish, change the index of refraction and make the angles come forward.

the nature of light 3

Like the waves of water the waves of light are capable of mixing – try it at the overhead projector in the exhibition.

When waves from different places collide new patterns are made – the waves interfere with one another. The phenomenon is called interference.

In fact it was Thomas Young who proved that light is waves – make the experiment on the following pages.

The nature of light 3

Polarized light – i.e. waves of light which are arranged to move in a single plane – can be made by using special filters. A pair of Polaroid sunglasses removes unpleasant reflections of sunlight

slide11

Interference occurs when two or more waves from different sources collide. Special patterns of interference may be created. Try to make patterns of interference by moving the frames.

laser

Lasers are applicable to a lot of things – CD players, printers, pointers, bar code readers, measuring, surgery and at cutting metal. A laser was also used to measure the distance to the Moon.

Laser light has only one colour (one wavelength) – it is called monochromatic light. Laser light is very concentrated i.e. it contains a lot of energy in a small area and is slightly scattered - even at long distance. Laser light is composed by phased light waves – the light waves “accompany each other” or “cohere”.

To understand the laser you must consider the light as particles – photons. Inside the laser there is a state where a photon with certain energy (a certain wavelength) starts an avalanche. This avalanche makes more photons of exactly the same kind to dash between two mirrors (S1 and S2) and release new photons. The mirror (S2) let some of the light through (about 1%) – the light which represents the laser ray.

Laser
slide13

A comparison between laser light and ordinary light. Press the bulb and see the refraction of the light in the prism. Press the symbol for the laser. Try to vary the wavelength

slide14

This is how a laser works. The photons are capable of penetrating one mirror. Try to see the photons without inducing energy. Then try to press the “Energy Pump” – now you have a real laser

colours 1

When the sunlight is refracted through a prism a spectrum of colours appears: red, orange, yellow, green, blue, indigo blue and violet. The physician Newton proved this by an experiment in 1676. He proved that sunlight is composed of all colours - and by addition white light occurs. Therefore sunlight is the most authentic light in which colours can be distinguished.

The different colours are characterised by differences in wavelength. We perceive the colour of an object by the reflection of the light from the object. The colours are made in our eyes and the brain converts certain wave lengths of light into what we define as colour. From birth on we are programmed to absorb the separate light waves and convert them into a colours via the brain. If a man perceives colours differently from most people he is colour-blind.

Colours 1
colours 2

When coloured light is blended - the primary colours are red, green and blue (RGB) – it is known as additional colour blending. When you mix red, green and blue light the result is white light.

Colours 2

When mixing paint the primary colours are: cyan, magenta and yellow (CMYK) – it is known as subtractive colour blending. .

The blending of coloured light – additive colour blending – therefore result in lighter colours, while the blending of paint – subtractive colour blending – result in progressively darker colours.

When blending colours you often use a colour wheel. There are several different types .

slide17
Additive colour blending – blending of coloured light.

You may blend the colours by moving them with the mouse.

slide18
Subtractive colour blending – blending paint of different colours.

You may blend the colours by moving them with the mouse.