Transcript www.PhysicsGCSE.co.uk P1d(ii) Light and Lasers You will learn about: Total Internal Reflection (TIR) How optical fibres are used in medicine and communications www.PhysicsGCSE.co.uk Critical Angle Recall that the.

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P1d(ii) Light and Lasers
You will learn about:
Total Internal Reflection (TIR)
How optical fibres are used in medicine
and communications
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Critical Angle
Recall that the angle of incidence, θi is measured from the
Normal.
If the angle of incidence is SMALLER than the critical angle the light
will refract through the material.
If the angle of incidence is EQUAL to the critical angle the light will
refract at 90° to the Normal along the boundary.
If the angle of incidence is LARGER than the critical angle the light
will totally internally reflect within the material.
For TIR to occur within a fibre optic cable you can see that the
angle of incidence has to be greater than the critical angle.
Normal
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Fibre Optics
REMEMBER:
If the light did not undergo total internal reflection (TIR)
then the light signal would not reach the receiver.
Light can be trapped within many materials such as water, perspex or
more commonly glass.
The light can be trapped because these materials are more dense than
the surrounding air, and, the light is reflected at the boundary between
the material and the air.
An optic fibre is a SOLID thin piece of glass. They are used because they
are very flexible and relatively cheap to make.
You can see that many signals can be sent through fibre optic cables.
This is very useful for communication purposes.
All of the light inside the fibre optic is reflected through it.
TOTAL…
INTERNAL…
REFLECTION
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Endoscopy
Endoscopes utilise the technology of fibre optics.
Doctors are able to use an endoscope to see inside the body without surgery.
Keyhole surgery can now also utilise the same technology.
Light passes along the outer fibres
and lights up inside the body at the
end of the manoeuvrable tip.
DIRECTION
OF LIGHT
Light is reflected by the body and
passes down the inner fibres to the
eyepiece which the Doctor is
looking through.
REMEMBER:
Within the endoscope the light travels by TIR.
The light exits the endoscope.
The light reflects off the body.
Some of that light enters into the inner fibre of
the endoscope.
This light, by TIR, travels to the eyepiece.
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Questions
1. What is the law that links the angle
of incidence and the angle of
reflection?
2. Use this image to explain how a fish
is able to see another larger fish
behind it.
3. Light travels through a glass block.
It reaches the glass-air boundary
with an angle of incidence of 30°. If
the critical angle for this glass is 42°
state what happens to the light.
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Questions
1.
2.
3.
What is the law that links the angle of incidence
and the angle of reflection?
Angle of Incidence = Angle of Reflection
or
θi = θr
Use this image to explain how a fish is able to
see another larger fish behind it.
Light from the larger fish totally internally
reflects at the water-air boundary and
reaches the eye of the fish in front.
Light travels through a glass block. It reaches the
glass-air boundary with an angle of incidence of
30°. If the critical angle for this glass is 42° state
what happens to the light.
The angle of incidence is smaller than the
critical angle so the light will refract. It will
leave the glass block and enter the air.