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Ch. 7 Looking At Light by Mind Map: Ch. 7 Looking At Light
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Ch. 7 Looking At Light

We will use this mind map to produce a study guide for the exam next Tuesday.

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Hyperopia

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Long-sightedness

If you have long-sightedness you are unable to see objects at a short distance.

7.9 light history

Aristotle-thought sound and light moved about in waves

Sir Isaac Newton-Newton found that light did shine through a vacuum. he claimed the light was made up of particles he called 'corpuscles'. Newton used his particle theory to explain why light reflected.his logic is that when these corpsuscles hit a surface,they simply bounced of like a tennis ball.

Thomas young-he became fascinated by the fact that the eye could create all colours just by looking at three diferent colours.

Evangelista Torricelli- succeeded in creating the vacuum.

7.1 Riding on a Light Beam

Rays

Narrow beams of light

Beam

Wide stream of light rays, all moving in the same direction

Reflection

Bouncing off the surface of a substance

Scattering

The sending of light in many directions by small particles within a substance. Blue light is scattered more than other colours, causing the sky to appear blue.

Transparent

Describes a substance that allows most light to pass through it. Objects can be seen clearly through transparent substances.

Translucent

Describes a substance that allows only some light to pass through it. It is possible to make out large shapes through translucent substances, but objects cannot be seen clearly.

7.5 Improving your image

Myopia

Short-sightedness

Astigmatism

In optics, astigmatism is when an optical system has different foci for rays that propagate in two perpendicular planes. If an optical system with astigmatism is used to form an image of a cross, the vertical...

Cataracts

7.8 seeing in colour.

absorbed

when white light falls on any surface, some colours are reflected while others are absorbed, a red surface aborbs all of the colours except red. only red light is reflected, same ewith green substance abosorbs all of the colours except green. this happens with blue as well a blue subtance absorbs all colours exvept blue.

primary colours

Red, Green and blue light can be combined to produce white light. these colours can produce all other colours thats why they are called primary colours., the coloured images that you see on tv or comptuer screens are produced by hundreds of narrow red, green and blue., Blue, Green and red can be combined to produce white light.

secondary colours

colours made by mixing primary colours are called secondary colours

colour in print.

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7.4 Its the Image that Counts

Retina/ Eye Diagram

This screen, called the retina, is lined with sight receptors called rods and cones

The Tree

The image formed on the retina is upside down, but the brain sees it the right way up

Optic Nerve

light-sensitive cells respond to light by sending signals to your brain through the optic nerve

The Iris/ Pupil

On its way to the lens, the light travels through a hole in the coloured iris called the pupil., The iris is a ring of muscle which controls the amount of light entering the lens.

Getting Things In Focus

The light coming from a nearby object needs to be bent more than the light coming from a distant object. The lens in your eye becomes thicker when you look at nearby objects., The shape of the lens is controlled by the ciliary muscles. When you look at distant objects, these muscles are relaxed and the lens is thin. When you look at nearby objects, the ciliary muscles contract. The suspensory ligaments become slack, causing the lens to bulge.

too close for comfort

summing up

when light meets a boundary between two different substances, it can be reflected, refracted or transmitted

you can see beams of light only when particles in substances like air scatter some of the light towards your eyes

Everything that you see is an image

when light travelsfrom water into the air, it bends away from the normal

a bioconvex lens is curved outwards on both sides. It converges light towards a point called a focus

when light travels from one substance into another, it changes speed and, unless it crossed the boundary at right angles, changes direction as well.

the action of the lens in obtaining a sharp image of the retina is called accomadation

A diverging lens spreads light out

if the combined focusing power of the lens and cornea is too weak for the length of the eye, images of nearby objects become blurry. this condition is commonly known as long sightedness

Most of the bending of light done by the human eye occurs at the cornea.

the total reflection of light when it travels from glass into air is called total internal reflection

Endoscopes, which include bundles of optic fibres, can be used to look in side the human body

the separation of white light in to its colours, called dispersion, occurs because different colours of light are bent by different amounts as they refract

Red, green and blue light can be combined together to produce white light

the colours yellow, magenta and cyan are used in printing, paints and dyes because they can be combined in different proportions to produce a wide range of colours including white

The receptor cells on the retina detect the brightness and colour of light. It is the cone cells that respond to colour

7.3 through the looking glass

Image - an iconic mental representation; "her imagination forced images upon her too awful to contemplate"

Diverging lens - a lens that causes parallel light rays to diverge.

Bioconcave - Having both sides concave

Converging Lens - A lens with a positive focal length which bends parallel rays of light toward a specific point, the focal point.

biconvex - convex on both sides, as a lens.

Focal - cause to converge on or toward a central point; "Focus the light on this image"

focal length - the distance from a focal point of a lens or mirror to the corresponding principal plane

Virtual focus -parallel beam focuses behind the mirror

7.6 Science & Technology

A Look inside

Optical Fibres, The optical fibres are made so that light is unable to emerge from the side of the glass fibres.

Endoscopes, Endoscopes can be also used for laser surgery. Intense laser beams can be directed into the optical fibres.

Inside Optical Fibres, Different type of endoscope includes:, • Gastroscopes, Which are used to examine the stomach and other parts of the digestive system, • Arthroscopes, Which are used to search for problems in joints like shoulders and knees, • Bronchoscopes, Which are used to see inside lungs

Communicating with visible light

Opical fibres, Optical fibres are used to transmit sound and images over ling distance., They are smaller, lighter, more flexible and more effcient than the electrical cables previously used for long-distance., Telephone, radio and TV comminication.

Laser beam

Electrical signals, Electrical signals from a microphone, television camera, computer or fax machine are converted into plues of light and transmitted along an optical fibre.

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