Light

Question 1

What is the relationship between refracted index, n, the angle of incidence and the angle of refraction (Snell’s law)?

Answer 1

n = sin(i) / sin(r)

Question 2

What is the relationship between critical angle (c) and refractive index (n)?

Answer 2

Sin (c) = 1/n

Question 3

What happens if a ray of light hits the centre (the normal) of a curved Perspex block and hits the straight side?

Answer 3

No change of direction because it hits the block at 90 degrees so the angle of incidence is 0 degrees

Question 4

What happens if a ray hits the flat surface of the circular Perspex block at an angle of incidence of 20 degrees?

Answer 4

It’s reflected out the other side of the block

Question 5

What is the critical angle?

Answer 5

Angle of incidence at a boundary with a less dense medium for which the angle of refraction is 90 degrees

Question 6

What happens where the angle of incidence is greater than the critical angle?

Answer 6

The ray is reflected from the inside surface of the glass (this is total internal reflection)

Question 7

Why does have refractive index have no unit?

Answer 7

It is a ratio

Question 8

Is the image from a periscope, upside down or the right way up when reflecting off 2 prisms?

Answer 8

Upside down, each time it hits the prism (mirror) it reflects 90 degrees. So as there are 2 prisms, it reflects a total of 180 degrees.

Question 9

What are the 7 colours that are refracted in a light spectrum from least refractive onwards?

Answer 9

Red, orange, yellow, green, blue, indigo, violet

Question 10

How are colours in the visible spectrum separated using a prism?

Answer 10

Dispersion

Question 11

Why does dispersion occur?

Answer 11

As a result of refraction

Question 12

If a colour in dispersion has a high frequency, what happens to the speed that light travels in the medium?

Answer 12

It slows down

Question 13

If a colour in dispersion has a high frequency, what happens to the speed that light travels in the medium?

Answer 13

It slows down

Question 14

What type of waves are light waves?

Answer 14

Transverse, they can be refracted and reflected

Question 15

What is the law of reflection?

Answer 15

The angle of incidence is equal to the angle of reflection (i=r)

Question 16

What is the difference between a wave entering a new medium when slowing down / speeding up?

Answer 16

Slowing down = bends towards the normal
Speeding up = bends away from normal

Question 17

How does light enter an optical fibre?

Answer 17

At an angle that is greater than the critical angle

Question 18

What is an optical fibre made of?

Answer 18

An inner core of glass, surrounded by a cladding of less dense glass

Question 19

What happens when light hits the boundary between the core and cladding in an optical fibre?

Answer 19

Under goes total internal reflection

Question 20

What pattern does light follow in an optical fibre?

Answer 20

Zigzag

Question 21

What are optical fibres used for?

Answer 21

Communications (broadband, internet, or phone)
Endoscopes (medical purposes), Decorative lamps

Question 22

What are advantages of optical fibres?

Answer 22

Cheap, lightweight, carry a large amount of information, can travel a long way without needing to be amplified

Question 23

What happens if a ray is shone into a right-angle triangular prism?

Answer 23

It is reflected 90 degrees