Understanding Light and Sight

7/27/2019 Understanding Light and Sight

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.7 UNDERSTANDING LIGHT AND SIGHT

PROPERTIES OF LIGHTLight is a form of energy that travels at the speed 300,000,000m/s. Approximately7.5 rounds of the earth in 1 second. Light travels in a straight lines within the same

medium (or medium with the same optical density). Light is reflected when it hits anopaque surface. Light is reflected when it travels from one transparent medium toanother.

REFLECTION OF LIGHTLight which falls on an opaque object may be absorb or reflected. Reflection takesplace when light rays which fall on the surface of an opaque object bounces off it.The amount and direction of the reflected light depend on the type of surface thelight fall on.

Incident

ray is theray oflight thatapproaches thesurface.Reflectedray is theray oflight thatbounces

off thesurface ofan object.

Rough and uneven surfaces such as cloth andwood (right) cause diffused reflection (lightreflection is scattered.Smooth and flat surfaces such as mirrors, glassand shinny metals (left) cause regular reflection(light reflected regularly).

Application of reflection of light in daily life

Plane mirrors are used in bathrooms or bedrooms. Side mirrors and rear-viewmirrors are used in cars. Convex mirrors give wider scope of view and used assecurity mirrors in shop and fish-eye mirrors at road bends. Concave mirrors

magnify images and are used in microscopes and telescopes. Periscopes are usedto see above the water surface in submarines. A periscope consists of two planemirror and change the direction of light. Kaleidoscopes form colourful images. Theyare made from two or more plane mirrors which reflect the light from objects placedbetween the mirrors.
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convex mirror used in a supermarket

Kaleidoscopes forkids

View of pattern inside kaleidoscopes

REFRACTION OF LIGHTLight can travel through transparent media such as air, water and glass. Lighttravels at different speeds in different media. When light travels from one mediuminto another, the change in the speed of light causes the light to bend orchangedirection. The refraction of light is the bending of light as light travels throughtwo types of media that have different densities (optical density). The speed of lightincreases when light enters a less dense medium meanwhile the speed of lightdecreases when light enters a denser medium. Refraction of light does not occurwhen the light ray is directly perpendicular to the surface of the medium (the lighttravel into the medium in the direction of the normal line), the light will pass through

the medium in a straight line.
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The refraction of light ray

Phenomenon of refraction oflight. The pencil which is inwater appear bended to the

observer.

Phenomenon of refraction oflight. Scuba diver appear

closer to the observer when it

is in the water.

VISION DEFECTS AND WAYS TO CORRECT THEM

An image is focused exactly on the retina for a person with normal vision. Thecommon defects of vision are : short-sightedness, long-sightedness, astigmatism,colour blindness and presbyopia.
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Light ray whichenter a normal eyewill be focus on the

retina.

Short-sightedness (can not view clearly for far object) the lightfocus in front of the retina

long-sightedness (can notview clearly for near

object) the light focus atthe back of retina

SHORT-SIGHTEDNESS (MYOPIA)

When someone suffer from short-sightedness has the condition ofunable to see the distant objectsclearly. The two causes: the eyelens is too tick and the eyeball istoo long. Therefore, light from distantobject is focused in front of the retina(as shown in the diagram above). Thecorrection method is to wear glasseswith concave lenses. The lensesdiverge light rays before they enter the

eye to form a sharp image on theretina.

The black line illustrate the situation of light been focus infront of the retina. The red line illustrate the situation of light

after passing through the concave lens and undergoesdivergence, then been focus on the retina.
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The black line illustrate the light ray which been focused at the back of the retina. The redline illustrate the situation of light after passing through the convex lens and undergoes

convergence, then been focused on the retina.

LONG-SIGHTEDNESS(HYPERMETROPIA)

When someonesuffer from long-sightedness hasthe condition ofunable to seethe near objectsclearly. The twocauses: the eyelens is too thinor the eyeball istoo short.

Therefore, lightfrom distantobject is focusedat the back ofthe retina (asshown in thediagram above).The correctionmethod is towear glasseswith convexlenses. Thelenses convergelight rays beforethey enter theeye to form asharp image onthe retina.

Example of Astigmatic cornea (cornea forpeople who suffer from Astigmatism)

Vision for people who suffer from Astigmatism.A blur image due to multiple focus point cause

by the irregular surface of the cornea.

ASTIGMATISMAstigmatism

is caused bythe irregularsurface ofthe cornea orlens or both.The eye isunable tofocus objectsinto a single,sharp image.Therefore,

the imagesseen by
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astigmaticpatient aredistorted andnot clear. Tocorrect the

situation, thepatient haveto wearglasses withcylindricallenses, wearspecialcontactlenses orundergoessurgery.

COLOUR BLINDNESSDue to shortage of conecells on the retina. Most ofthe people who suffer fromcolour blindness can notdifferentiate between redand green colours. Thesituation can not becorrected because it ishereditary.

People with colour blindness can not read "8" from the picture, because they

can not differentiate green dots and red dots.

LIMITATIONS OF SIGHTWe can not seemicroscopic objects,distant objects, we can notsee through opaqueobjects and when the lightfall on the blind spot.

Blind Spot

Let the computer screen be 30cm from your eyes. Focus on the rabbit andclose your right eye. Move closer to the screen in a straight line. At some

point the magic hat will lost from your view.

OPTICAL ILLUSION
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DEVICES USED TO OVERCOME THE LIMITATIONS OF SIGHT

Electron Microscope-which is much more powerful

compare to light microscope

Image of flea after been magnify by 86xunder electron microscope.

MICROSCOPE

Aninstrumentwhichmagnifiestiny(micro)objects

such asbacteria(microorganism)or cells.Uses twoconvexlenses: theobjectivelens and theeyepieces

lens.
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This is a much more advance telescope whichcan catch better image compare with thetelescope with tripod stand on the right

TELESCOPETelescope is an opticalinstrument used by humanbeing to explore the deepspace. In order for us to have

a better idea regarding ourspace, we need to keepimproving our technologythrough optical physic studywhich learn aboutelectromagnetic wave (light).HUBBLE TELESCOPEHubble-Telescope is the mostadvance telescope whichever been build by humanbeing. Below show some

photo caught by using HubbleTelescope.

Telescope to viewthe sky.
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Part of Hubble Telescopewhich been launch into

space and spin in the orbit

The image caught by

Hubble Telescope.

The imagecaught by

HubbleTelescope.

With our eyes, we can only see this.

STEREOSCOPIC VISION AND MONOCULAR VISION
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Rabbit categorized as monocular vision animal; Monkey categorized as stereoscopic animal.

MONOCULAR VISION- The field of vision in both eyes eitherdo not overlap or may

overlap only a little.- It gives a wider field of vision.Monocular vision sometimes

covers 360.- It does not form a three-dimensionalimage.

- Not able to estimate the positions anddistances accurately.- Prey have monocular vision.- It enables prey such as deer and goatsto detect predatorsfrom any angle.

STEREOSCOPIC VISION- The field of stereoscopic vision is the areawhere the visual

fields of both eyes overlap- It gives a smaller field of vision.- it forms a three-dimensional image.- Able to estimate the position and distanceof an objectmore accurately.

- Human beings and predators havestereoscopic vision.- It enables predators such as owls andtigers to determineaccurately the position of their prey.

1.8 SOUND AND HEARINGSound is a form of energy. Sounds are produced by vibrations. When an objectvibrates, kinetic energy is changed to sound energy. Musical instruments like theguitar and violin produce sound through vibrations.
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Tuning fork producesound when it vibrate.

Sound is form of wave, and it need mediumto travel.

Guitar produce sound, when the stringsvibrate.

THE NEED FOR A MEDIUM FOR SOUND TO TRAVEL

Sound needs a medium to travel. Sound can travel trough solids, liquids andgases. Sound cannot travel through a vacuum. Sound travels fasterthrough solidsthan through liquids. This is because particles are arranged closely in solids. Theycan pass on vibration quickly. Sound travels the slowest through gases because the

particles are arranged loosely. Therefore, the transfer of vibrations occurs slowly.
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Understanding Light and Sight

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