Refraction of light (Unit 2)

Question 1

Refractive Index of a medium? equation

Answer 1

c / v

Question 2

In the refractive index equation, what is C?

Answer 2

Speed of light in a vacuum, 3x 10^8

Question 3

In the refractive index equation, what is v?

Answer 3

Speed of light in the medium

Question 4

Snells law? equation 2

Answer 4

n1 v1= n2 v2
n1 sin θ= n2 sin θ

Question 5

What does Snell’s law say about when light goes into a material with a HIGHER refractive index into a material with a LOWER refractive index?

Answer 5

-When light goes into a material with a HIGHER refractive index (more dense)into a material with a LOWER refractive index (less dense)
- the angle of INCIDENCE is SMALLER than the angle of refraction

Question 6

What does Snell’s law say about when light goes into a material with a LOWER refractive index into a material with a HIGHER refractive index?

Answer 6

When light goes into a material with a LOWER refractive index (less dense) into a material with a HIGHER refractive index (more dense)
-the light bends TOWARDS the normal (Incidence > refractive)

Question 7

What can show Snells law?

Answer 7

-Wave model of light propagation, the plane waves approaching a plane boundary obliquely, and being refracted

Question 8

What are the conditions for total internal reflection?

Answer 8

-The wave must be travelling from a material with a higher refractive index to a lower refractive index.
-The angle of incidence must be larger than the CRITICLE angle

Question 9

Critical angle equation?

Answer 9

N1 sinθ = n2

Question 10

Critical angle equation (derivation)?

Answer 10

-Since θ2 is equal to 90 degrees
- sin 90 = 1
- so we can write n1 sinθ = n2

Question 11

How can light can travel from one end of the wire to the other, even when the fibre is not straight?

Answer 11

-Due to total internal reflection taking place within the core
-the rays of light hit the boundary an angle larger than the
critical angle therefore will reflect, so the signal will travel along the fibre to the end

Question 12

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

Answer 12

-As for total internal reflection to occur
-light must travel from a material with a higher refractive index to a lower refractive index
-the angle of incidence must be greater than the critical angle.

Question 13

What is the problem of multimode dispersion with optical fibres?

Answer 13

-as the signals are sent through the fibre at different angles, they will travel through different distances through the fibre
-this means the time they take to travel will also be different, as they travel at the same speed
- As signals are sent as coded pulses, this will cause a problem if there is too much of a range of distances within a fibre. A pulse will become spread and, if the pulses are
too close, they will overlap, making the signal unclear

Question 14

How has the introduction of MONOMODE FIBRES helped?

Answer 14

-very narrow cores, of which the diameters are only a few wavelengths.
-there is only one possible path through the fibre and therefore the pulses do not spread or overlap.
- signals can be sent a greater distance and at a greater rate without becoming muddled.

Question 15

How does light change direction in prisms?

Answer 15

-total internal reflection