Refraction

Question 1

Refraction

Answer 1

When the wave changes its direction and speed as they move through one medium to another.

Question 2

Refractive index

Answer 2

The ratio of the speed of light in a vacuum to the speed in the material medium.
Refraction index in air = 1

Question 3

Refraction index equation

Answer 3

n = c /v
c = speed of light in a vacuum (m/s)
v = speed of light in a medium (m/s)
Sin(i)/sin(r) = n

Question 4

Kinds of Material

Answer 4

Transparent material: Air, water, glass, plastic
Opaque material: Wood, sand, stone, metal
The transparent material is used for refraction and the opaque for reflection.

Question 5

Total internal reflection

Answer 5

When a light ray reaches the boundary between two transparent materials it may be refracted. if it is leaving the more dense medium the refraction would move away from the normal.
But this would bend the ray at more than 90degrees form the normal, the refraction is not possible and it will reflect internally, with no energy getting out (Total internal reflection)

Question 6

TIR only occurs

Answer 6

• The light travels from dense medium to a less dense medium e.g. glass to air.
• The angle of incidence in the dense medium is greater than the critical angle.
• If the angle of refraction in the air becomes 90 degrees the angle of incidence in the glass is called the critical angle.
• If the angle of incidence in the glass is greater than the critical angle, total internal reflection occurs (i = r).

Question 7

Optic fibre

Answer 7

They are very long thin cylinders of glass or sometimes plastic. They are used to transfer information from one place to another.

Question 8

Optic fibre pt2

Answer 8

Information is coded into a digital signal as pulses of light. These pules travel down the optical fibre and are decoded on the other side.

Question 9

TIR in the Optic fibre

Answer 9

The light travels down the inside of the tube due to the total internal reflection. This is because when the light hits the boundary between the core and the cladding, it is trying to go from a slow to fast medium so it then bends away from the normal.

Question 10

Critical angle

Answer 10

When the wave hits a boundary between two materials, the angle of refraction would be at 90 degrees (travelling across the boundary), making the angle of incidence the critical angle.
SinC = 1/n

Question 11

Internal reflection

Answer 11

When a wave that is already in a dense medium, hits the boundary with a less dense medium and energy is reflected back into the denser medium.

Question 12

The core

Answer 12

It is where the fibre transmits the light down the tube.

Question 13

The cladding

Answer 13

Covers the core keeping the light in the tube, which makes it have a lower refraction causing it to have total internal reflection.

Question 14

The sheath

Answer 14

It protects the bundle of fibres from damage.

Question 15

The buffer

Answer 15

Protects an individual fibre from damage and helps to identify the fibres.