Waves and optics

Question 1

Define longitudinal waves

Answer 1

In longitudinal waves, the vibrations are parallel to the direction of wave travel

Question 2

Define transverse waves

Answer 2

In transverse waves, the vibrations are at right angles to the direction of wave travel.

Question 3

Define amplitude

Answer 3

A waves maximum displacement from it’s equilibrium position

Question 4

Define frequency

Answer 4

The number of waves that pass a point in a unit time
f= 1/T

Question 5

Define period

Answer 5

Time takes for a wave to complete a cycle
T= 1/f

Question 6

Define wavelength

Answer 6

The distance between two identical positions on two adjacent waves (eg. peak to peak)

Question 7

What type of waves polarise?

Answer 7

Only transverse waves

Question 8

The EM spectrum:
Which has the highest wavelength?
Which has the highest frequency?

Answer 8

Radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, gamma rays
Highest wavelength: Radio
Highest frequency: Gamma

Question 9

What conditions are necessary to produce a stationary wave?

Answer 9

Two waves travelling in opposite directions along the same line of travel and in the same plane.
The waves have the same speed.
The waves have the same frequency.
The waves have the same approximate amplitude.

Question 10

Define interference
(vs superposition?)

Answer 10

When two waves meet while travelling along the same medium and interact. It is observed.
Superposition is the sum of the displacements. It is the effect.

Question 11

What makes two waves coherent?

Answer 11

In phase
Constant phase difference
Similar amplitudes

Question 12

For constructive interference to occur, what must the phase difference be?

Answer 12

nλ

Question 13

For destructive interference to occur, what must the phase difference be?

Answer 13

(n+1/2)λ

Question 14

In double slit diffraction, what effect does increasing the distance between the slits and the screen cause?

Answer 14

Increasing fringe width
w = λD/s

Question 15

In double slit diffraction, what effect does increasing the slit seperation cause?

Answer 15

Decreasing fringe width
w = λD/s

Question 16

What does white light look light when diffracted through a single slit?

Answer 16

Bright white central maxima, then black fringes alternating with rainbow fringes either side. For the rainbow fringes, red light is furthest from maxima, and the blue light is closest to maxima.

Question 17

For a diffraction grating, what is the key equation?

Answer 17

dsinx =nλ

Question 18

What is refraction?

Answer 18

When light slows down/speeds up and then changes direction

Question 19

What is Snells law?

Answer 19

n1sinx1 = n2sinx2

Question 20

When travelling into a more optically dense material, what happens to the light?

Answer 20

It will bend towards the normal

Question 21

When travelling into a less optically dense material, what happens to the light?

Answer 21

It will bend away from the normal

Question 22

When does total internal reflection occur?

Answer 22

When the angle of refraction is greater than 90°, the angle of incidence is greater than the critical angle and n1>n2

Question 23

How can you work out the refractive index of a substance?

Answer 23

n = c / cs
Where c is the speed of light in a vacuum and cs is the speed of light in the substance

Question 24

How can you work out the critical angle?

Answer 24

sin xc = n2/n1

Question 25

Angular frequency equation?

Answer 25

w=2 pi f