Waves (Higher)

Question 1

Define ‘refraction’

Answer 1

The change in speed (and generally direction, also) when a light crosses a boundary between two materials.

Question 2

Light travels from air into glass. What happens to the direction in which it is travelling?

Answer 2

It bends towards the normal. (Unless it is travelling along the normal, in which case it continues in a straight line)

Question 3

Light travels from glass into air. What happens to the direction in which it is travelling?

Answer 3

It bends away from the normal. (Unless it is travelling along the normal, in which case it continues in a straight line)

Question 4

Light travels from glass into air. What happens to the speed at which it is travelling?

Answer 4

It speeds up

Question 5

Light travels from air into glass. What happens to the speed at which it is travelling?

Answer 5

It slows down

Question 6

Light travels from glass into air. What happens to the frequency of the light waves?

Answer 6

The frequency of the light does not change

Question 7

Light travels from air into glass. What happens to the frequency of the light?

Answer 7

The frequency of the light does not change

Question 8

Light travels from air into glass. What happens to the wavelength of the light?

Answer 8

The wavelength of the light decreases

Question 9

Light travels from glass into air. What happens to the wavelength of the light?

Answer 9

The wavelength of the light increases

Question 10

Glass has a refractive index of 1.5, water has a refractive index of 1.33, emerald has a refractive index of 1.6. In which of these materials does light travel the fastest?

Answer 10

The lower the refractive index of a material, the faster the speed of light in that material. So light travels faster in water than in glass of emerald.

Question 11

For diamond, n = 2.42. For olive oil, n = 1.47.

In which of these two materials does light travel slower?

Answer 11

‘n’ stands for the material’s refractive index. Since the refractive index is higher for diamond, this means light travels more slowly in diamond.

Question 12

What equation is referred to as ‘Snell’s law’?

Answer 12

n = sin(i) ÷ sin (r)

Question 13

In the equation
n = sin(i) ÷ sin (r)
what does ‘i’ stand for?

Answer 13

Here, ‘i’ stands for the ‘angle of incidence.’

Question 14

In the equation
n = sin(i) ÷ sin (r)
what does ‘r’ stand for?

Answer 14

Here, ‘r’ stands for the ‘angle of refraction.’

DON’T confuse this with the reflection equation, where r stands for ‘the angle of reflection’

Question 15

When does total internal reflection occur?

Answer 15

When light approaching a boundary has an angle of incidence that is greater than the critical angle.
(So when i > c, for light approaching the boundary)

Question 16

What is the critical angle?

Answer 16

It is the angle of incidence that gives a refracted ray which travels at 90° to the normal.

Question 17

What equation can be used to calculate the critical angle?

Answer 17

sin(c) = 1÷n

Question 18

In the equation
sin(c) = 1÷n
what does ‘c’ stand for?

Answer 18

The critical angle (for a particular material)

Question 19

Thin strands of glass or plastic can be used for communication, to carry a light signal. What is the name of these thin strands?

Answer 19

Optical fibres

Question 20

What effect allows infrared light to travel within an optical fibre? (2 marks)

Answer 20

Repeated (1 mark) total internal reflection (1 mark)

Question 21

Name three applications of total internal reflection.

Answer 21

Optical fibres
Binoculars
Periscopes (with right angled prisms)
…all rely on total internal reflection.

Question 22

Name two uses of optical fibres

Answer 22

Used in communication, to carry light signals.

Used in endoscopes, allowing doctors to look inside the human body.