Unit 2 - Refraction of Light

Question 1

What is refraction

Answer 1

when light enters a denser transparent material and changes speed and direction

Question 2

Which lense focuses light?

Answer 2

convex

Question 3

which lens diffracts light into a spectrum of colours?

Answer 3

prirm

Question 4

which lens causes the light to diverge (go into diff directions/separate)

Answer 4

concave

Question 5

What is the normal

Answer 5

dotted line drawn 90 degress to the surface it enters

Question 6

what is a particle of light called

Answer 6

photon

Question 7

What is the speed of light in a vaccume?

Answer 7

3x10⁸ m/s

Question 8

What is the refractive index of a medium?

Answer 8

its the ratio of the speed of light in a vaccume to the speed of light in that medium.

Question 9

What is the angle of incidence

Answer 9

The angle between the incident ray and the normal at the point of incidence

Question 10

What is the angle of refraction

Answer 10

The angle between the refracted ray and the normal at the point of incidence where refraction occurs

Question 11

What is the angle of reflection

Answer 11

The angle between the reflected ray and the normal at the point of incidence to a reflecting surface.

Question 12

What is the criticle angle

Answer 12

it is the certain angle of incidence, where the refracted ray is bent through an angle of 90 degrees from the normal so that it just grazes the block.

Question 13

What is total internal reflection (TIR)

Answer 13

it is when the angle of incidence is greater than the criticle angle, meaning all of the light is reflected by the boundary. No light leaves through the surface by refraction. Therefore this is called the total internal reflection, because the ray is reflected inside the block.

Question 14

What are optical fibers

Answer 14

fibers which transfer data using light and total internal reflection. it is surrounded by glass core, cladding, buffer and jacket.

Question 15

Describe the core, cladding, buffer and jacket of the optical fiber

Answer 15

Core
-glass with a higher index of refraction than the cladding
-carries the signal

Cladding
-Glass or plastic with a lower index of refraction than the core

Buffer
-Protects the fiber from damage
moisture

Jacket
-holds one or more fibers in a cable

Question 16

Why must the cladding have lower refractive index than the core?

Answer 16

For TIR to occur

lower refractive index means refraction occurs until criticle angle, so the total internal reflection occurs.

Question 17

What happens to the light in an optical fibre

Answer 17

incident angle is bigger than criticle angle, so TIR occurs, light is totaly internally reflected across the optical fibre

Question 18

What are multimode optical fibres

Answer 18

Same as optical fibre but have multiple paths (the mode) of light travelling within them.

Question 19

Advantage and Disadvantage of multimode fibres

Answer 19

Advantage
-less expensive to operate, install and maintain than single-mode cables

Disadvantage
-much more limited in speed and distance

Question 20

What is multimode dispersion

Answer 20

Because different paths are taken, the modes (individual paths) have different propagation velocities (diff wave movements) Meaning that the signal does not arrive at the same time and appears distorted which is called multimode dispersion.

Question 21

Why are multimode fibres only effective over short distances

Answer 21

so that multimode dispersion effect is smaller, as the pulses will begin to overlap.

Question 22

What are monomode optical fibres

Answer 22

Very thin cores. Only have 1 single node which is parallel to the wire through the center. These have higher data transfer rates and can transfer data over much longer distances because there is little multimode dispersion.

Question 23

what is the main difference between monomode and multimode fibres

Answer 23

in monomode, the core is so small that only 1 mode can pass through, No total internal reflection occurs. Angle to axis is zero.

Question 24

Advantages and disadvantages of monomode fibres

Answer 24

Advantage
-faster and covers more distance than multimode fibre
Disadvantage
-More expensive to produce and operate than multimode fibre

Question 25

Stand proud,

Answer 25

You are strong.

Question 26

Define diffraction

Answer 26

The spreading out of waves when they meet obstacles such as the edges of a slit. Some of the waves energy travels into geometrical shadows of the obstacles

Question 27

What type of material will cause light to refract

Answer 27

By entering a more dense transparent medium, or leaving a that medium to a less dense medium