Report Sheet 1 What is Internal Reflection?
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Information from Source 1) (copy and paste from website, book or magazine)
Total internal reflection, in physics, complete reflection of a ray of light within a
medium such as water or glass from the surrounding surfaces back into the medium.
The phenomenon occurs if the angle of incidence is greater than a certain limiting
angle, called the critical angle. In general, total internal reflection takes place at the
boundary between two transparent media when a ray of light in a medium of higher
index of refraction approaches the other medium at an angle of incidence greater
than the critical angle. For a water-air surface the critical angle is 48.5°. Because
indices of refraction depend on wavelength, the critical angle (and hence the angle
of total internal reflection) will vary slightly with wavelength and, therefore, with
colour. At all angles less than the critical angle, both refraction and reflection occur
in varying proportions.
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Key words from Source 1
Total internal reflection, medium, water, glass, surrounding surfaces, angle of incidence, critical angle, two transparent media, higher index of refraction, wavelength, varying proportions.
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In your own words summarise relevant information from website, book or magazine
Total internal reflection occurs when the angle of incidence is greater than the critical angle. Total internal reflection takes place at the boundary of two transparent media’ when the incidence ray shines through the medium with an angle of incidence greater than the critical angle. Different surfaces change the critical angle, and because indices of refraction depend on wavelength the critical angle will change size slightly.
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Report Sheet 2 How internal reflection is used in everyday life?
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It is due to the phenomena of 'total internal reflection'. On a very hot day in a desert, the air just in contact with sand
is hotter than the air above it due to the high temperature of sand. This causes the refractive index of the air in
contact with the sand to be lower than that of the air above it. Thus, sunlight passes through a medium of higher
refractive index to that of lower refractive index.
At a particular angle, the angle of incidence becomes greater than the critical angle and all the conditions of total
internal reflections are fulfilled. This causes the sunlight to reflect from the interface of both the air columns itself
without touching the sand. Hence, it appears as a watery surface from far off distances, also known as mirage.
While going nearer to the apparent water, the angle of incidence of sunlight decreases and becomes less than the
critical angle. So, total internal reflection does not occur for that point at that angle and hence the mirage disappears.
Mirage is thus visible only when the distance from a point is greater than a critical distance determined by the
refractive index of the air columns to satisfy the condition of critical angle for total internal reflection to occur.
When light passes from one medium into a second, less dense medium, the light bends away from the normal. At a particular incident angle, the angle of refraction will be 90 degrees, and the refracted ray would travel along the boundary between the two media.
Source 2
The incident angle at which this occurs is called the critical angle. This angle can be calculated by using Snell's Law:
sin(critical angle) = (n2/n1)(sin 90 degrees) = (n2/n1)
Where n1 = index of refraction in 1st medium
n2 = index of refraction in 2nd medium
If the angle of incidence is increased beyond the critical angle, the light rays will be totally reflected back into the incident medium. This effect is called total internal reflection. But note that total internal reflection cannot occur if light is traveling from a less dense medium to a denser one.
Source 3
Most of our discussion of refraction in this unit has pertained to the refraction of light at a distinct boundary. As light is transmitted across the boundary from one material to another, there is a change in speed, which causes a change in direction of the light wave. The boundaries that we have been focusing on have been distinct interfaces between two recognizably different materials. The boundary between the glass of a fish tank and the surrounding air or the boundary between the water in a pool and the surrounding air are examples of distinct interfaces between two recognizably different materials.
It has been mentioned in our discussion that the refraction or bending of light occurs at the boundary between two materials; and once a light wave has crossed the boundary it travels in a straight line. The discussion has presumed that the medium is a uniform medium. A uniform medium is a medium whose optical density is everywhere the same within the medium. A uniform medium is the same everywhere from its top boundary to its bottom boundary and from its left boundary to its right boundary. But not every medium is a uniform medium, and the fact that air can sometimes form a non-uniform medium leads to an interesting refraction phenomenon - the formation of mirages.
Refraction in a Non-Uniform Medium
A mirage is an optical phenomenon that creates the illusion of water and results from the refraction of light through a non-uniform medium. Mirages are most commonly observed on sunny days when driving down a roadway. As you drive down the roadway, there appears to be a puddle of water on the road several yards (maybe one-hundred yards) in front of the car. Of course, when you arrive at the perceived location of the puddle, you recognize that the puddle is not there. Instead, the puddle of water appears to be another one-hundred yards in front of you. You could carefully match the perceived location of the water to a roadside object; but when you arrive at that object, the puddle of water is still not on the roadway. The appearance of the water is simply an illusion.
Mirages occur on sunny days. The role of the sun is to heat the roadway to high temperatures. This heated roadway in turn heats the surrounding air, keeping the air just above the roadway at higher temperatures than that day's average air temperature. Hot air tends to be less optically dense than cooler air. As such, a non-uniform medium has been created by the heating of the roadway and the air just above it. While light will travel in a straight line through a uniform medium, it will refract when traveling through a non-uniform medium. If a driver looks down at the roadway at a very low angle (that is, at a position nearly one hundred yards away), light from objects above the roadway will follow a curved path to the driver's eye as shown in the diagram below.
Light that is traveling downward into this less optically dense air begins to speed up. Though there isn't a distinct boundary between two media, there is a change in speed of a light wave. As expected, a change in speed is accompanied by a change in direction. If there were a distinct boundary between two media, then there would be a bending of this light ray away from the normal. For this light ray to bend away from the normal (towards the boundary), the ray would begin to bend more parallel to the roadway and then bend upwards towards the cooler air. As such, a person in a car sighting downward at the roadway will see an object located above the roadway.
Source 4
Imagine you're in the desert. You're lost. You've been walking for hours. You've run out of water. On the horizon, you see a giant, shimmering puddle of water. "Yippeeeeeeeeee", you shout. You're saved!
But...it's not a puddle of water. It's a mirage.
Mirages are optical illusions that have fooled many thirsty explorers. Take a look at this video:
How do mirages form?
Normally, light waves from the sun travel straight through the atmosphere to your eye. But, light travels at different speeds through hot air and cold air.
Mirages happen when the ground is very hot and the air is cool. The hot ground warms a layer of air just above the ground.
When the light moves through the cold air and into the layer of hot air it is refracted (bent).
A layer of very warm air near the ground refracts the light from the sky nearly into a U-shaped bend. Our brain thinks the light has travelled in a straight line.
Our brain doesn't see the image as bent light from the sky. Instead, our brain thinks the light must have come from something on the ground.
You can even see mirages in the UK. Have you ever seen a wet looking shimmer above tarmac on a hot day? That's the beginning of a mirage.
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Key words from Sources
Mirage, Optical, air heat, angle of incidence, critical angle, light rays, light waves, sun, atmosphere, eye, speed, hot air, sand, refraction of light, optical density, hot air, cold air, refracted.
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In your own words summarise relevant information from website, book or magazine
Mirages occur when the light rays of the sun are bent, due to the ground being hot and the air being cold, when the ground is hot it warms the air above it, this causes it to be denser and refracts the light rays, this happens because of optical density, giving it a high index of refraction, it slows the light ray down allowing it to bend and create the optical illusion. Our brain doesn’t see the light rays as bent, so it projects the image of water to try and fix the light rays we see. This happens because of the critical angle, at a certain distance, the light rays reach your eyes, but if you are to move closer, it disappears because the critical angle no longer exists at that point.
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Total internal reflection occurs when the angle of incidence is greater than the critical angle. Total internal reflection takes place at the boundary of two transparent media, when the incidence ray shines through the medium with an angle of incidence greater than the critical angle. Different surfaces change the critical angle, and because indices of refraction depend on wavelength the critical angle will change size slightly.
These two phenomenons occur because if total internal refraction.
Mirages occur when the light rays of the sun are bent, due to the ground being hot and the aire being cold, when the ground is hot it warms the air above it, this causes it to be denser and refracts the light rays, this happens because of optical density, giving it a high index of refraction, it slows the light ray down allowing it to bend and create the optical illusion. Our brain doesn't see the light rays as bent, so it projects the image of water to try and fix the light rays we see. This happens because of the critical angle, at a certain distance, the light rays reach your eyes, but if you are to move closer, it disappears because the critical angle no longer exists at that point.
Unlike mirages, diamonds have a different effect with the different angles.
Because diamonds have a high refractive index, total internal refraction or reflection can occur, this occurs because of the position of the incidence ray/angle. If the diamond is strategically cut, it is able to have total internal refraction or reflection. The angle of incidence is moved and the reflected ray will bounce out the top, IF it is strategically cut. If it isn't strategically cut it will refract AND reflect into different angles, this is because the critical angle is acting here.
Task C:
Total internal reflection is seen all the time in everyday life, this phenomenon is changed using
mediums, the density of the medium, if the medium has a high refractive index, like plastic, it will
slow a beam of light and cause it to turn slightly, as soon as it leaves this medium, it will turn the
other way slightly again. If the medium has a low refractive index, like air, it will not change the
speed of the beam and it will continue forward.
mediums, the density of the medium, if the medium has a high refractive index, like plastic, it will
slow a beam of light and cause it to turn slightly, as soon as it leaves this medium, it will turn the
other way slightly again. If the medium has a low refractive index, like air, it will not change the
speed of the beam and it will continue forward.
Mirages and diamonds are created and use this in everyday life.
Mirages occur when the light rays of the sun are bent, due to the ground being hot and the air
being cold, when the ground is hot it warms the air above it, this causes it to be denser and
refracts the light rays, this happens because of optical density, giving it a high index of refraction,
it slows the light ray down allowing it to bend and create the optical illusion. Our brain doesn’t see
the light rays as bent, so it projects the image of water to try and fix the light rays we see. This
happens because of the critical angle, at a certain distance, the light rays reach your eyes, but if
you are to move closer, it disappears because the critical angle no longer exists at that point.
being cold, when the ground is hot it warms the air above it, this causes it to be denser and
refracts the light rays, this happens because of optical density, giving it a high index of refraction,
it slows the light ray down allowing it to bend and create the optical illusion. Our brain doesn’t see
the light rays as bent, so it projects the image of water to try and fix the light rays we see. This
happens because of the critical angle, at a certain distance, the light rays reach your eyes, but if
you are to move closer, it disappears because the critical angle no longer exists at that point.
Unlike mirages, diamonds use their own medium, not heated air.
Because diamonds have a high refractive index, total internal refraction or reflection can occur,
this occurs because of the position of the incidence ray/angle. If the diamond is strategically cut, it
is able to have total internal refraction or reflection. The angle of incidence is moved and the
reflected ray will bounce out the top, IF it is strategically cut. If it isn't strategically cut it will refract
AND reflect into different angles, this is because the critical angle is acting here.
this occurs because of the position of the incidence ray/angle. If the diamond is strategically cut, it
is able to have total internal refraction or reflection. The angle of incidence is moved and the
reflected ray will bounce out the top, IF it is strategically cut. If it isn't strategically cut it will refract
AND reflect into different angles, this is because the critical angle is acting here.
The advantages and disadvantages of internal reflection.
Advantages of internal reflection include, being able to zoom in with a camera due to the light
bending, but this also can be a disadvantage because the signal then becomes low. Internal
reflection is something we use everyday, using it in optical fibers to send large amounts of
information long distances using glass or mirrors to reflect it. This helps us get information around
more effentically and quickly. This is also done in an endoscope, using a medium to redirect the
light so the user can see inside the interior of organ and cavities within the body, this can help a
patient survive possible illnesses.
bending, but this also can be a disadvantage because the signal then becomes low. Internal
reflection is something we use everyday, using it in optical fibers to send large amounts of
information long distances using glass or mirrors to reflect it. This helps us get information around
more effentically and quickly. This is also done in an endoscope, using a medium to redirect the
light so the user can see inside the interior of organ and cavities within the body, this can help a
patient survive possible illnesses.
Using this can also cause things to come out as different, or wrong all together, because of optical
illusion like a mirage, our brain may not register it as correct and it will try replacing whatever is
missing or seems wrong with something that seems more logical.
illusion like a mirage, our brain may not register it as correct and it will try replacing whatever is
missing or seems wrong with something that seems more logical.
