Transcript PowerPoint version

PHYSIC PROJECT
LIGHT
By Maria Ahmed
Contents:
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What is Light ?
Reflection and Refraction
Mirrors and Lenses
Diffraction and
Interference
Speed of Light
Electromagnetic Spectrum
Pictures
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.
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 red
color, it has the longest wavelength.
Light consists of photons which carry energy of light. The longer
wavelength, the less photons.
About Light Speed
Light travels fast. In a vacuum it moves about 3 x 108 meters (186,000 miles) each
second, a distance so large it’s difficult to comprehend. Here are some roughly
equivalent distances:
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Eight times around Earth’s equator
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Most of the way from Earth to the moon
SHADOW
Use a light projector for an example. We can see light spread out
all round on the wall. But when something blocks part of the
beam. The part will show black.
 It is because light is made up of millions of rays. Each individual
ray travels in a straight line, when something blocked the ray, it
cannot reach the screen and results in shadow
REFLECTION
Reflection
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
waves are allowed to return "intact", without being disturbed. But,
if the reflective surface is not a smooth one, what is 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 Reflection
Total 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.
Refraction
Refraction 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.
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Refraction and Color Separation
When light is refracted, the amount that the light bends depends
on its wavelength. Light waves with short wavelengths are bent
more than light waves with long wavelengths. You have already
learned that white light is composed of all the colors of visible
light. You also know that the different colors correspond to
different wavelengths. Because of this, white light can be
separated into different colors during refraction, as shown in the
figure below. Color separation during refraction is partially
responsible for the formation of rainbows. Rainbows are created
when sunlight is refracted by water droplets.
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
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
the new substance,
the perpendicular to
that spot is referred
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 Lenses
Mirrors 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 length.
Mirrors can create both real and virtual images, real being images
that are actually there, virtual images only being able to be seen by
looking into the mirror. Images are also either inverted or erect,
upside down or right side up respectively.
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The focal length is referred to as F and the radius of
curvature 2F. The magnification of any mirror can be
calculated by subtracting the ratio of the height 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
the object..
Types 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 bends
further away in the middle than at the edges, like the inside of
bowl. The image produced is dependent on the 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
concave mirror, bending further away at the edges than in the
middle like the outside of a bowl. Convex mirrors always 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 to
the focal length and the radius of curvature. The images formed
are similar to the concave mirrors.
A concave lens is a diverging lens which works
similar to the convex mirror. This lens is thicker
towards the edges and thin in the middle and are
used in helping correction of nearsightedness. All
images produced by concave lenses are virtual,
erect, and reduced.
Picture
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
ceiling.
Object is crystal
ball
Light reflected in circles
onto the ceiling
Torch is
Light source
Mirror Reflection
This picture shows how an image is
reflected from from a mirror. Virtual image
by a plane mirror.
Angle of reflection is equal to
The angle of incidence.This Law
Explains why mirrors can
form images.
Mirror Reflection (2)
In a plane mirror, the image
Is virtual, upright, the same
Size as the object, and is far
Behind the mirror as the
Object infront.
Image of
Object
Original Object
Pencil in Glass
Picture. Shows a pencil placed in a glass of water. The
pencil appears to be broken or bent, due to the different
index of refraction in water.
Pencil appears
broken
Broken Pencil (2)
Pencil in water
appears To be bent due
to refraction
Broken Pencil
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Another Picture to show refraction in
water.
Appears to
Be bent
Light Reflection
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This picture shows the reflection of the mirror on the ceiling
Reflection
Mirror
Experiments Done
The Attached document shows the procedures carried out for doing
experiments to see the concepts of Light reflection and refraction.
EXPERIMENT
Please see attached word document on disk.
CITATION:
TextBooks
Giancoli, Douglas: Physics for Scientists & Engineers, Third Edition. Prentice Hall
Zitzewits, Paul : Physics Principles and Problems. Merril
Websites:
Demonstration from Professor Brooks site: Refraction and Reflection:
http://lectureonline.cl.msu.edu/%7Emmp/kap25/Snell/app.htm
Physics Central Online : http://www.physicscentral.com/
American Institute of Physics: http://www.aip.org/
American Scientists:
http://www.americanscientist.org/articles/99articles/Parker.html
THE END