Category Light and Lasers

What is Laser light?

It punches through steel. It pierces diamonds. It performs tiny, delicate operations. Is it a superhero? No, it is a special kind of light. The light that can do these things is called a laser beam. A laser beam is made up of bundles of energy called photons, just like ordinary light. But the photons in a laser beam act in an unusual way.

The photons in ordinary light have different amounts of energy. They go in all directions, and they start and stop at different times. They are like people in a crowd, walking in all different directions. But in laser light, all the photons work in the same way. They are exactly the same colour, so they all have the same amount of energy. They are also given off at regular times, and they travel in only one direction. They are like marchers in a parade.

With all the photons moving together, laser light is very powerful. But don’t worry! You aren’t going to run into any laser beams out on the street. Laser beams have to be made in special machines. Then they can burn through metal or even drill a tiny hole in a diamond.

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What is Laser and it’s major types?


A laser is a device that creates an intense beam of light called a laser beam. A laser beam is monochromatic: it is made up of light of just one colour of the spectrum. This means that all the light waves in it have the same wavelength. Just as importantly, all the waves are “in phase”, which means that as they leave the laser, their crests and troughs all line up with each other.

The lasing material is contained in a tube with a mirror at one end and half-silvered mirror at the other. Light bounces up and down, gaining strength until it is powerful enough to break out.

The word “laser” is short for Light Amplification by Stimulated Emission of Radiation. Inside the laser is lasing material, which can be a solid, a liquid or a gas. The atoms of the material are excited or “stimulated” by giving them energy, either in the form of light or electricity. This makes them emit light (a type of radiation), which in turn makes other atoms emit light of the same wavelength. This process creates an intense laser beam. The wavelength and so the colour, of a laser beam depends on the lasing material. Some lasers produce ultraviolet or infrared radiation rather than visible light. The first working laser was built by American physicist Theodore Maiman in 1960.

A high-power laser is being used to perform eye surgery. If the retina, the part of the eye that contains light-sensitive cells, becomes detached, a laser beam can stick it back in place.


The most common uses of lasers are playing compact discs and reading bar codes. These lasers are normally red lasers that use semiconductor lasing materials. They are low-power lasers, but they are still dangerous to look at directly. Low-power lasers are also used in communications, where they send signals along optical-fibre cables, in laser printers, in surveying, and for light shows. High-power lasers can be focused to create intense heat in materials. They are used in manufacturing for accurate cutting and in medicine for delicate surgery.

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Define Light and explain its main features?


Light is a kind of energy. It is the form of energy that our eyes can detect, enabling us to see. It is produced by very hot things – the Sun, fire and the tiny wire inside electric light-bulbs. Certain animals also have light-producing organs.

Light from the Sun is essential to life on Earth. Some creatures live off minerals in the ocean depths but these are exceptions. Most plants use sunlight to make their food. All plant-eating animals, together with other animals that eat plant-eaters, also therefore depend on sunlight.

Light rays can only travel in straight lines. If they strike an object which does not allow light to pass through it (an opaque object), a shadow is cast on the unlit side. Light can be reflected, however. Light reflected from objects allows us to see them. Light rays strike and bounce off a flat, shiny surface like a mirror at the same angle. This enables us to see our reflection.


When we switch on an electric light, it seems that the room is filled with light instantaneously. But light rays do take time to travel from their source. They travel extremely quickly: about 300,000 kilometres (or seven-and-a-half times around the world) per second in outer space. The speed of light is, in fact, the speed limit for the Universe: nothing can travel faster. Light waves are able to travel through empty space – a vacuum – whereas sound waves cannot. Light actually moves less quickly through air, water or glass than through empty space.

Because stars are very far from Earth – at least thousands of billions of kilometres – astronomers measure their distances in light years, the amount of time it takes for light to travel to us from them.


Light rays bend, or refract, when they pass through different transparent materials. This is because light travels at different speeds through different materials. At the boundary between two materials, for example, air and water, the light changes speed slightly and is refracted from its straight path. You can see this effect when looking at the bottom of swimming pool. It looks much shallower than it really is.


A lens, a shaped piece of glass or plastic, can bend light, either spreading it out or bringing it closer together. A convex lens, one that is thicker in the middle than at the edge, brings light rays together at a single point called a focus. The eye contains a natural convex lens which focuses an image on to the retina at the back of the eye. If you hold a convex lens so that the object you are looking at lies between the lens and the focus, the object will appear larger and further from the lens than it really is. A simple magnifying glass is a convex lens, and is useful for studying minute detail as, for example, on a postage stamp or a tiny insect or flower.

A concave lens is the opposite of a convex lens: it is thicker around the edge than in the middle. This kind of lens diverges (spreads out) light rays. It is used in glasses to correct short-sightedness.

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How can I make my own periscope?

This periscope is made from a box containing two mirrors held at 45°. It can reflect light so that you can see over walls and around corners!

What you need

Two small mirrors (both the same size), some card; a protractor for measuring the angles of the mirrors; a ruler; a pencil; scissors; sticky tape; and a box of paints.

Measure the distances shown as ‘a’ and ‘b’ in the diagram. Make sure that the mirror is held at an angle of 45° while you do this (a protractor will help).

The casing

Now you can draw the pattern for your periscope onto the card. Make sure you use the measurements you have just taken. You can make the periscope as tall as you like. Cut around the outline of the pattern. Now draw two rectangles onto your box — like the ones in the diagram. Cut these out to make two openings. Fold the box into shape and hold the edges together with sticky tape.

Fixing the mirrors

Your two mirrors should fit into opposite corners of the box with their shiny sides facing the openings. Use strips of card to keep the mirrors in place, whichever way up you hold the periscope. Decorate the box as you choose. Your periscope is now ready to use. Just look into the bottom opening and see what you can see!

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What are various uses of Lasers?

Lasers are one of the most important developments in recent years. There are many ways in which lasers can be used. As well as making good cutting tools in industry, lasers make excellent ‘knives’ for surgeons. The laser ‘knife’ is completely sterile and seals small blood vessels as it cuts, so that less blood is lost. Laser light is often used to ‘weld’ a retina, which has become detached, to the back of the eye.

Holograms are three-dimensional pictures made by illuminating objects with laser light. They look solid and real. They are used on credit cards as they are very difficult to forge.

Lasers are used in the aviation industry.

Lasers are often used in medicine, particularly in delicate surgery.

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How do light and lasers are related?

Light waves

Light travels in waves — but what is a wave? You can make a wave by shaking one end of a ribbon. The up and down movement you make spreads along the length of the ribbon and appears as a wave. A wave is a way in which energy can move from one place to another. Light waves travel at an astonishing speed, faster than anything else we know.

The distance between the top of one wave and the next is known as the ‘wavelength’. The depth of a wave is called its ‘amplitude’. Each colour of the spectrum has its own special wavelength and amplitude.

Measuring with light

Both large and small distances can be measured very accurately with laser light. In 1969, the Apollo II astronauts placed a mirror on the Moon. Scientists on Earth shone a laser beam towards the mirror and timed how long it took for the beam to be reflected back again. They knew the speed at which the light travelled and so they were able to work out the distance of the Moon from the Earth — to within just a few centimetres of the actual distance!

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What is Laser Light?

We have seen that white light is a mixture of many colours which can be separated. It helps to think of these colours as waves. Each different colour of light has a different length of wave. Red light has long waves. Blue light has short waves. However, the light produced by a laser is the entire same wavelength.

This means that a beam of light produced by a laser can be easily concentrated onto a tiny point. It can produce enough heat to turn a metal into a vapour! Lasers can be used as accurate cutting tools which can even cut through diamond, the hardest substance known.

Laser light and wavelength

White light from a torch can be thought of as a mixture of waves. Each wavelength represents a certain colour. The waves making up a laser beam are quite different.

Not only are all the waves the same length (colour), but they are lined up so that the tops (peaks) of the waves coincide.

The various wavelengths making up white light can be separated by a prism. We know that laser light is all of one wavelength because it cannot be separated by a prism.

Waves of laser light are all bent to the same extent by the prism since they all travel at the same speed through glass.

Beams of laser light are powerful enough to cut through metal.

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What are Lenses and how they are used?

Lenses are pieces of transparent material, such as glass or plastic, which have been made into special shapes. They refract (bend) light in certain ways depending on their shape. Lenses may be convex or concave. Convex lenses are thicker in the middle than they are at the edges. Concave lenses are thinnest in the middle.

A convex lens

Light rays from a small, close object travel in straight lines to the lens. But as they pass through the lens and towards your eye, they bend inward. Since your brain expects light to travel in straight lines, you see a magnified (larger) image.

A concave lens

Rays of light from a tennis ball travel in straight lines to the lens. As they pass through the lens, they bend outward towards your eyes. Again, the brain expects these rays to have arrived in straight lines and you see a smaller image.

Convex and concave lenses are very useful. They are found in many of the instruments which help us to see things which we could not see with our eyes alone. Lenses are used in telescopes which help us see stars and planets, in binoculars which enable us to watch birds and animals in the wild, and in microscopes which magnify tiny living things.

People use lenses to carry out detailed work.

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How does mixing of coloured light happen?

You are seeing the light it is reflecting. It is reflecting sunlight or electric light, both of which are ‘white’. Yet you can see many different colours. You must remember that white light is really a mixture of colours. The white part of the page is reflecting all the colours of the spectrum. But the printed words are reflecting almost no light. Black is the absence of colour, or light. The colours we see depend on the type of light being reflected. Red, green and blue are known as the primary light colours. It is possible to make any colour by mixing different amounts of these colours.

You can see some of the effects of mixing the primary colours of light. Red and green together make yellow light; green and blue combine to make cyan; and blue and red give magenta. Any other colour can be produced by varying the amounts of each of the primary colours. Red, blue and green together make white.


Red, blue and yellow are said to be the primary colours of paint. Blue paint reflects green light as well as blue. Yellow paint reflects green and red light. A mixture of blue and yellow paint appears green since this is the only colour reflected by both. An artist can mix paints to produce any colour.

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How do we see?

It is light which enables our eyes to see. Light reflected from this page enters each eye and passes through a hole called the ‘pupil’. In dim surroundings, your pupils get larger to let in more light. In bright light, they become smaller.

Your eyes each contain a lens. This lens is jelly-like and can change shape. The lens bends the light entering your eyes so that you always see a clear picture. At the back of the eye is the ‘retina’. When light rays fall onto the retina, they cause messages to be sent to the brain. Your brain interprets the messages it receives and you are conscious of ‘seeing’.

Opticians use different lenses to check a patient’s eyesight.

The pinhole camera

This simple camera is a box with a pinhole at the front. Rays of light from the candle travel in straight lines through the pinhole to the screen at the back. The rays cross over as they pass through the hole and so the image is formed upside down.

Hold the camera between you and the candle. Look at the tracing paper — you will see an upside down candle!

The eye works a little like the pinhole camera. An apple held in your hand reflects rays of light which pass through your eye. The lens becomes short and fat to focus the light rays onto your retina.

To focus on the apple tree, your lens gets longer and thinner. The image formed on your retina is upside down in both cases. When the information is relayed from your retina to your brain, you ‘see’ things the right way up.

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