PHYSIC PROJECTPHYSIC PROJECT

LIGHTLIGHT

By Maria AhmedBy Maria Ahmed

Contents:Contents:

What is Light ?What is Light ? Reflection and RefractionReflection and Refraction Mirrors and LensesMirrors and Lenses Diffraction and Diffraction and

InterferenceInterference Speed of LightSpeed of Light Electromagnetic SpectrumElectromagnetic Spectrum PicturesPictures

Light is a form of energy just like heat and sound. It is given Light is a form of energy just like heat and sound. It is given off as a result of atoms within a substance being given energy.off as a result of atoms within a substance being given energy.

The main source of light is the sun. Early people rubbed woods or stones to make light. Nowadays, we

can generate light from electricity.

Light have different wavelengths to have different colors. For Light have different wavelengths to have different colors. For red color, it has the longest wavelength.red color, it has the longest wavelength.

Light consists of photons which carry energy of light. The longer Light consists of photons which carry energy of light. The longer wavelength, the less photons.wavelength, the less photons.

About Light SpeedAbout Light Speed

Light travels fast. In a vacuum it moves about 3 x 10Light travels fast. In a vacuum it moves about 3 x 1088 meters (186,000 miles) each meters (186,000 miles) each second, a distance so large it’s difficult to comprehend. Here are some roughly second, a distance so large it’s difficult to comprehend. Here are some roughly equivalent distances:equivalent distances:

Eight times around Earth’s equator Eight times around Earth’s equator Most of the way from Earth to the moon Most of the way from Earth to the moon

SHADOWSHADOWUse a light projector for an example. We can see light spread Use a light projector for an example. We can see light spread

out all round on the wall. But when something blocks part out all round on the wall. But when something blocks part of the beam. The part will show black.of the beam. The part will show black.

It is because light is made up of millions of rays. Each It is because light is made up of millions of rays. Each individual ray travels in a straight line, when something individual ray travels in a straight line, when something blocked the ray, it cannot reach the screen and results in blocked the ray, it cannot reach the screen and results in shadowshadow

REFLECTIONREFLECTION

ReflectionReflection

By looking at the surface of water, we can see a clear image when the water is smooth; and a jumble of scattered

image can be seen when the water is ruffled by wind. •Do you know why?

Reflection is the returning, or "bouncing" of a wave off of a surface which resists that kind of wave. When it reflects, it

always does so at the exact same angle it came in at.

If you shine a light 45 degrees to the left, it will exit 45 degrees to the right. The angle at which the light comes in is called the angle of incidence, while the angle at which it exits

is called the angle of reflection.

This observation is called the scientific law of reflection, which states that the angle of incidence is equal to the

angle of reflection and opposite sides of the normal – an imaginary line at right angle through the point where the

rays meet.

A reflection coming off a smooth surface is sharp, because the A reflection coming off a smooth surface is sharp, because the waves are allowed to return "intact", without being disturbed. waves are allowed to return "intact", without being disturbed.

But, if the reflective surface is not a smooth one, what is But, if the reflective surface is not a smooth one, what is called diffuse reflection occurs. called diffuse reflection occurs.

This is because different parts of the light hit the surface in different places at different depths and different times. This

results in a mostly blurred image, which is why rough, grainy surfaces do not reflect images well.

Total Internal ReflectionTotal Internal ReflectionTotal internal reflection is a

special case of reflection created when when a light passes from a

more optically dense medium to a less dense one at an angle such that there is no refracted ray.

This how optical fibers work, the fibers are specifically constructed to produce this effect,

preserving the intensity of the light as it passes through the fiber to its destination.

RefractionRefractionRefraction is the change in direction of a wave when it passes into

a new substance.

The reason the light changes direction or "bends" is because each different substance has it's own effect on the speed of light

within itself.

Every substance has an optical density

called the substance's index of refraction, is how well light passes through it, the higher

the density, the harder time light has moving through it.

Refraction and Color SeparationRefraction and Color Separation When light is refracted, the amount that the light bends depends When light is refracted, the amount that the light bends depends

on its wavelength. Light waves with short wavelengths are bent on its wavelength. Light waves with short wavelengths are bent more than light waves with long wavelengths. You have already more than light waves with long wavelengths. You have already learned that white light is composed of all the colors of visible learned that white light is composed of all the colors of visible light. You also know that the different colors correspond to light. You also know that the different colors correspond to different wavelengths. Because of this, white light can be different wavelengths. Because of this, white light can be separated into different colors during refraction, as shown in the separated into different colors during refraction, as shown in the figure below. Color separation during refraction is partially figure below. Color separation during refraction is partially responsible for the formation of rainbows. Rainbows are created responsible for the formation of rainbows. Rainbows are created when sunlight is refracted by water droplets.when sunlight is refracted by water droplets.

This index can be determined by taking the ratio of the speed This index can be determined by taking the ratio of the speed of light in a vacuum (3x106 km/s) and the speed of light in the of light in a vacuum (3x106 km/s) and the speed of light in the

substance. substance.

It can also be found by taking the ratio of the sine of the angle of incidence and the angle of refraction,

similar to the angles mentioned above. This equation is called Snell's Law.

Where the light hits Where the light hits the new substance, the new substance, the perpendicular to the perpendicular to that spot is referred that spot is referred to as the normal. to as the normal.

If the new substance has a higher index of refraction than the substance the light was in, the ray of light will be bent towards the normal. Conversely, if the new substance is

of a lower optical density, the light will bend away from the normal.

Mirrors and LensesMirrors and LensesMirrors and Lenses BasicsMirrors and Lenses Basics

Mirrors have reflective surfaces. Every mirror has a focal point, where all the light directed at that mirror

converges or diverges and the distance between the mirror and that point is called the focal length.

The radius of the curvature of a mirror is exactly twice the focal The radius of the curvature of a mirror is exactly twice the focal length. Mirrors can create both real and virtual images, real length. Mirrors can create both real and virtual images, real being images that are actually there, virtual images only being being images that are actually there, virtual images only being able to be seen by looking into the mirror. Images are also able to be seen by looking into the mirror. Images are also either inverted or erect, upside down or right side up either inverted or erect, upside down or right side up respectively. respectively.

The focal length is referred to as F and the radius of The focal length is referred to as F and the radius of curvature 2F. The magnification of any mirror can be curvature 2F. The magnification of any mirror can be calculated by subtracting the ratio of the height of the calculated by subtracting the ratio of the height of the image to the height of the object and the ratio of the image to the height of the object and the ratio of the distance from the mirror of the image to the distance of distance from the mirror of the image to the distance of the object.. the object..

Types of Mirrors and LensesTypes of Mirrors and Lenses

Plane mirrors are simple straight up mirrors. In a plane mirror, the image is always virtual and the same size but right side up as the object.

A concave mirror is a converging mirror. A concave mirror A concave mirror is a converging mirror. A concave mirror bends further away in the middle than at the edges, like the bends further away in the middle than at the edges, like the

inside of bowl. The image produced is dependent on the inside of bowl. The image produced is dependent on the positioning of the object being viewed in the mirror. positioning of the object being viewed in the mirror.

If the object is beyond 2F, the image is real, inverted, and reduced, at 2F real, inverted, the same height,

between F and 2F real, inverted, and magnified, at F there is no image, and closer then F the image is

virtual, erect, and magnified.

A convex mirror is a diverging mirror. This is the opposite of a A convex mirror is a diverging mirror. This is the opposite of a concave mirror, bending further away at the edges than in the concave mirror, bending further away at the edges than in the

middle like the outside of a bowl. Convex mirrors always middle like the outside of a bowl. Convex mirrors always produce virtual, erect, reduced images. produce virtual, erect, reduced images.

These do suffer from spherical aberration, which is why you cant see images well one a perfectly spherical

reflective surface. 

The image is changed by the position of the object in relation The image is changed by the position of the object in relation to the focal length and the radius of curvature. The images to the focal length and the radius of curvature. The images formed are similar to the concave mirrors.formed are similar to the concave mirrors.

A concave lens is a diverging lens which works A concave lens is a diverging lens which works similar to the convex mirror. This lens is similar to the convex mirror. This lens is thicker towards the edges and thin in the thicker towards the edges and thin in the middle and are used in helping correction of middle and are used in helping correction of nearsightedness. All images produced by nearsightedness. All images produced by concave lenses are virtual, erect, and concave lenses are virtual, erect, and reduced.reduced.

PicturePictureThis Picture shows the reflection of light from a light source. Holding a piece of This Picture shows the reflection of light from a light source. Holding a piece of

crystal and letting light pass through it reflected light in different parts of the crystal and letting light pass through it reflected light in different parts of the ceiling. ceiling.

Light reflected in circles onto the ceiling

Object is crystalball

Torch isLight source

Mirror ReflectionMirror ReflectionThis picture shows how an image is This picture shows how an image is

reflected from from a mirror. Virtual image reflected from from a mirror. Virtual image by a plane mirror.by a plane mirror.

Angle of reflection is equal to The angle of incidence.This Law

Explains why mirrors canform images.

Mirror Reflection (2)Mirror Reflection (2)

In a plane mirror, the imageIs virtual, upright, the same

Size as the object, and is farBehind the mirror as the

Object infront.

Image ofObject

Original Object

Pencil in GlassPencil in GlassPicture. Shows a pencil placed in a glass of water. The Picture. Shows a pencil placed in a glass of water. The

pencil appears to be broken or bent, due to the different pencil appears to be broken or bent, due to the different index of refraction in water.index of refraction in water.

Pencil appearsbroken

Broken Pencil (2)Broken Pencil (2)

Pencil in water appears To be bent due

to refraction

Broken PencilBroken PencilAnother Picture to show refraction in Another Picture to show refraction in

water.water.

Appears to Be bent

Light ReflectionLight Reflection This picture shows the reflection of the mirror on the ceilingThis picture shows the reflection of the mirror on the ceiling

Mirror

Reflection

Experiments DoneExperiments DoneThe Attached document shows the procedures carried out for doing The Attached document shows the procedures carried out for doing

experiments to see the concepts of Light reflection and refraction.experiments to see the concepts of Light reflection and refraction.

EXPERIMENTEXPERIMENTPlease see attached word document on disk.Please see attached word document on disk.

CITATION:CITATION:TextBooksTextBooks

Giancoli, Douglas: Giancoli, Douglas: Physics for Scientists & Engineers, Third EditionPhysics for Scientists & Engineers, Third Edition. Prentice Hall. Prentice Hall Zitzewits, Paul : Zitzewits, Paul : Physics Principles and ProblemsPhysics Principles and Problems. Merril. Merril

Websites:Websites:Demonstration from Professor Brooks site: Refraction and Reflection: Demonstration from Professor Brooks site: Refraction and Reflection:

http://lectureonline.cl.msu.edu/%7Emmp/kap25/Snell/app.htmhttp://lectureonline.cl.msu.edu/%7Emmp/kap25/Snell/app.htmPhysics Central Online : Physics Central Online : http://www.physicscentral.com/http://www.physicscentral.com/American Institute of Physics: American Institute of Physics: http://www.aip.org/http://www.aip.org/American Scientists: American Scientists:

http://www.americanscientist.org/articles/99articles/Parker.htmlhttp://www.americanscientist.org/articles/99articles/Parker.html

THE ENDTHE END