Download refraction

Total Internal Reflection
• Special case of Refraction!
Refraction of Light
• Example Problem #2
A ray of light enters the air from the water at
an angle of 50 degrees. What is the angle
of refraction?
Refraction of Light
• Example Problem #2
A ray of light enters the air from the water at
an angle of 50 degrees. What is the angle
of refraction?
n1 = 1.33
Refraction of Light
• Example Problem #2
A ray of light enters the air from the water at
an angle of 50 degrees. What is the angle
of refraction?
n1 = 1.33
θ1 = 50 degrees
Refraction of Light
• Example Problem #2
A ray of light enters the air from the water at
an angle of 50 degrees. What is the angle
of refraction?
n1 = 1.33
θ1 = 50 degrees
n2 = 1
θ2 = ?
Refraction of Light
• Example Problem #2
A ray of light enters the air from the water at
an angle of 50 degrees. What is the angle
of refraction?
n1(sin θ1) = n2(sin θ2)
Refraction of Light
• Example Problem #2
A ray of light enters the air from the water at
an angle of 50 degrees. What is the angle
of refraction?
n1(sin θ1) = n2(sin θ2)
1.33(sin 50) = 1 (sin θ2)
Refraction of Light
• Example Problem #2
A ray of light enters the air from the water at
an angle of 50 degrees. What is the angle
of refraction?
n1(sin θ1) = n2(sin θ2)
1.33(sin 50) = 1 (sin θ2)
θ2 = Error
Refraction of Light
• Example Problem #2
When you get error on your calculator, this
means something. This means that the
light does NOT refract (enter the new
medium), it must do something else.
Refraction of Light
• Let’s take a look at what happens as we
increase the angle of incidence
Refraction of Light
• Let’s take a look at what happens as we
increase the angle of incidence
Refraction of Light
• Look what happens to the ray at this
specific angle?
Refraction of Light
• Where do you think the light ray goes in
the right hand diagram???
Refraction of Light
• It does not enter the new medium, it
reflects off the surface (like skipping a
stone on the water)
Refraction of Light
• This phenomenon is called
TOTAL INTERNAL RELFECTION
Total Internal Reflection
• This occurs when you get ‘Error’ on your
calculator.
Total Internal Reflection
Total Internal Reflection
Total Internal Reflection
• This is also how fiber optics works. The
light is trapped inside.
Fiber Optics
•
Fiber optics (optical fibers) are long,
thin strands of very pure glass about
the diameter of a human hair.
– They are arranged in bundles called
optical cables and used to transmit
light signals over long distances.
•
If you look closely at a single optical
fiber, you will see that it has the
following parts:
– Core - Thin glass center of the fiber
where the light travels
– Cladding - Outer optical material
surrounding the core that reflects the
light back into the core
– Buffer Coating - Plastic coating that
protects the fiber from damage and
moisture
Fiber Optics
• The light in a fiber-optic cable travels through the
core by constantly bouncing from the cladding
due to total internal reflection.
– Because the cladding does not absorb any light from
the core, the light wave can travel great distances.
Total Internal Reflection
• This is what gives a diamond its luster.
The light gets trapped inside the diamond
and is only allowed to escape at certain
angles!
Diamonds are a Physicists Best
Friend
•The cut of the diamond must be
just right to get reflection from
the bottom facet.
•Too Shallow
•It Leaves
•Too Deep
•It Leaves
•Now it’s just right
Total Internal Reflection
• The surface acts like a mirror so it will
bounce off at the same angle it comes in
at.
Critical Angle
• What is the angle of incidence which is the
boundary between refraction and total
internal reflection?
Critical Angle
• This angle is called the CRITICAL ANGLE
Critical Angle
• Let’s calculate the critical angle (incidence
angle) when going from water to air.
θ2
n (air) = 1
θc
n (water) = 1.33
Critical Angle
n1 = 1.33
θc=?
n2 = 1
θ 2= 90
θ2
n (air) = 1
θc
n (water) = 1.33
Critical Angle
n1(sin θc) = n2 (sin θ2)
Critical Angle
n1(sin θc) = n2 (sin θ2)
1.33 (sin θc) = 1(sin 90)
Critical Angle
n1(sin θc) = n2 (sin θ2)
1.33 (sin θc) = 1(sin 90)
1.33 (sin θc) = 1(1)
Critical Angle
n1(sin θc) = n2 (sin θ2)
1.33 (sin θc) = 1(sin 90)
1.33 (sin θc) = 1(1)
(sin θc) = 1/1.33
Critical Angle
n1(sin θc) = n2 (sin θ2)
1.33 (sin θc) = 1(sin 90)
1.33 (sin θc) = 1(1)
(sin θc) = 1/1.33
θc = 48.8 degrees
Critical Angle
• So the equation ends up being
Sin өc = n2
n1
Critical Angle
• The critical angle when going from water
to air is 48.8 degrees
θ2
n (air) = 1
θc
n (water) = 1.33
Critical Angle
• This means if our angle of incidence is
less than 48.8 degrees, we will get
refraction.
Critical Angle
• This means if our angle of incidence is
greater than 48.8 degrees, we will get
total internal reflection.
Homework
• Do worksheet #2 in minipacket