Unit 2.6: Refraction of light

Question 1

When any type of wave encounters a barrier that it reflects from it always follows which simple rule?

Answer 1

incident angle, i = reflected angle, r

Question 2

There is a direct link between the incident and refracted angles for any one particular material or medium. This relationship is known as:

Answer 2

Snell’s law

Question 3

What is Snell’s law?

Answer 3

At the boundary between any two given materials, the ratio of the sine of the
angle of incidence to the sine of the angle of refraction is a constant.

Question 4

All media through which light travel through have what is called a…

Answer 4

Refractive index,n

Question 5

What is refractive index?

Answer 5

When waves travel from one medium to another its speed changes. The speed in one medium compared to the speed in a vacuum can be calculated using the
refractive index,n.

Question 6

State the equation for refractive index

Answer 6

n=c/v
n=refractive index of the medium
c=speed of light in a vacuum
v=speed of light in the medium

Question 7

When light passes between 2 mediums, we can use two equations. What are they?

Answer 7

n1v1=n2v2
n1Sinθ1=n2Sinθ2

Question 8

When does total internal reflection occur?

Answer 8

This phenomenon occurs when light moves from a more optically dense material (e.g. water) to a less optically dense material (e.g. air) causing a change in speed.

Question 9

What is the refractive index for air?

Answer 9

n=1

Question 10

When light moves from water into air, and the angle of incidence is less than the critical angle. What happens to the ray of light emerging from water?

Answer 10

the light ray refracts/ bends away from the normal as it emerges from the water

Question 11

When light moves from water into air, and the angle of incidence is equal to the critical angle. How does the ray of light act when travelling into air?

Answer 11

the light ray passes along the
surface of the boundary.

Question 12

When light moves from water into air, the angle of incidence is greater than the critical angle. How does the ray of light act when travelling into air?

Answer 12

It doesn’t travel into the air. the light ray is
reflected back into the water. This phenomenon is known as total internal reflection.

Question 13

How can we determine the critical angle?

Answer 13

Using Snell’s law
n1Sinθ1=n2Sinθ2

Question 14

What do optical fibres use to work?

Answer 14

Total internal reflection

Question 15

What is the inside of an optical fibre called?

Answer 15

The core

Question 16

What is the outside of the optical fibre called?

Answer 16

The cladding

Question 17

Which has a greater refractive index in an optical fibre, the core or the cladding and why?

Answer 17

The core. So the rays of infrared light are reflected back into the core as long as the angle is greater than the critical angle

Question 18

What is a monomode fibre?

Answer 18

Fibres with a core diameter so small that the only possible path through the fibre is along it’s axis (straight through the middle)

Question 19

What is a multimode fibre?

Answer 19

The infrared light in multimode fibres travel in zig-zag paths.

Question 20

When does TIR occur?

Answer 20

If the angle of incidence is greater than the critical angle. Travels towards a material with a lower refractive index

Question 21

Advantages of using monomode fibres over multimode?

Answer 21

Paths at different angles to the axis are of different lengths so data is not distorted when arriving.

Question 22

Which type of optical fibre is best suited for long distance communication?

Answer 22

Monomode

Question 23

How does using angles close to the critical minimise multimode dispersion

Answer 23

-It cuts down range of paths
-Less likelihood of overlapping