M4C4

Question 1

Name and describe the two types of progressive waves

Answer 1

• Transverse waves have particle motion that is perpendicular to the direction of wave propagation.
• Longitudinal waves have particle motion that is parallel to the direction of wave propagation.

Question 2

What are progressive waves?

Answer 2

Waves that transfer energy away from a source

Question 3

What is the wave equation?

Answer 3

v = f λ
v = velocity (m s^-1)
f = frequency (Hz or s^-1)
λ = wavelength (m)

Question 4

Define wavelength

Answer 4

The wavelength of a wave is the distance between two successive identical points that have the same pattern of oscillation. It is also the distance the wave travels before the pattern repeats itself.

Question 5

Define period (t)

Answer 5

The period of a wave is the time it takes for one complete pattern of oscillation to take place at any point.

Question 6

Define frequency

Answer 6

The frequency of a wave is the number of oscillations per unit time at any point and is related to the time period T by the equation f = 1/T

Question 7

Define displacement in terms of waves

Answer 7

Displacement is the distance any part of the wave has moved from its mean (or rest) position - it can be positive or negative.

Question 8

Define amplitude in terms of waves

Answer 8

Amplitude is the maximum displacement - the distance from a peak or trough to the mean (rest) position.

Question 9

Define phase difference

Answer 9

Phase difference concerns the relationship between the pattern of vibration at two points. Two points that have exactly the same pattern of oscillation are said to be in phase - there is zero phase difference between them.

Question 10

What is the equation for intensity?

Answer 10

I = P/A
I = intensity (W m^-2)
P = power output of the source (W or J s^-1)
A = area over which the radiation falls (m^-2)

Question 11

What is the formula for the speed of sound in air?

Answer 11

331+0.6T

T= temperature

Question 12

What’s the relation between intensity and amplitude?

Answer 12

intensity ∝ (amplitude)^2

Question 13

What is the refractive index equation?

Answer 13

refractive index = sin(i)/sin(r)
i = angle of index
r = angle of reflection

Question 14

Define diffraction

Answer 14

Changes in the directions of waves can also occur when they meet an obstacle, or as they pass through an aperture. This is called diffraction.
For maximum effect, the aperture needs to be the same size as the wavelength of the wave.

Question 15

Define interference

Answer 15

This occurs when two waves meet and occupy the same space at the same time.
Effectively they can add together to make a larger wave (peak + peak), or they can cancel each other out (crest + trough).
This adding and subtracting of waves causes an interference pattern.

Question 16

What are the properties of electromagnetic waves?

Answer 16

• travel through a vacuum.
  
  • interlocked magnetic and electrical waves at right angles to each other.
  • c = 3.0x108 m s-1 (or 2.98x108 m s-1).
  • transverse.
  • reflected, refracted and diffracted.
  • interference and polarisation.

Question 17

Whats the difference between x-rays and gamma rays

Answer 17

X-rays and gamma rays are often identical in terms of their energies, wavelength and frequencies. The only difference between them is how they are produced. X-rays are made by accelerated electrons outside the nucleus, but gamma rays are always emitted from the nucleus of an atom.

Question 18

What type of wave can be polarized?

Answer 18

Transverse

Question 19

What’s malu’s law?

Answer 19

When a perfect polariser is put in a beam of polarised light, the intensity, I, of the light that passes through it is given by I = Imaxcos^2 θ, where I is the intensity transmitted at angle θ. Also, Imax is the maximum intensity transmitted at θ = 0^o.
If the analyser is at right angles to the the polariser, then θ = 90^o and no light will pass through. This situation is known as ‘crossed Polaroids’

Question 20

What is the polarization equation?

Answer 20

I = Imaxcos2θ
Imax = the maximum intensity transmitted (at θ = 0^o).
θ = angle between the initial polarisation direction and the polariser axis of polarisation.

Question 21

What is the equation for finding the refractive index?

Answer 21

n = c/v
n = refractive index 
c = speed of light in a vacuum
v = speed of light in material

Question 22

What is Snell’s law?

Answer 22

n1sinθ1 = n2sinθ2
nsinθ = c
n1 = refractive index of first material
θ1 = angle light enters the first material
n2 = refractive index of the second material
θ2 = angle light enters the second material
n = refractive index
c = speed of light in a vacuum

Question 23

When does total internal reflection take place?

Answer 23

It occurs when the angle of refraction is above of equal to 90^o

Question 24

Define superposition

Answer 24

The adding together of the displacements of two waves.

Question 25

Define constructive interference

Answer 25

The result of two waves arriving at a single point in phase (ɸ = 0 o or 2𝜋 rad) with each other

Question 26

Define destructive interference

Answer 26

The result of two waves arriving at a single point in antiphase (ɸ = 180 o or 𝜋 rad) with each other

Question 27

Define coherence

Answer 27

When two waves have a constant phase difference, they are said to be coherent with each other

Question 28

Define path difference

Answer 28

The difference between the distances travelled by two waves arriving at the same point (measured in m)

Question 29

Define phase difference

Answer 29

The difference in the phases of two waves of the same frequency (measured in radians)

Question 30

What is the equation associated with the Young double slit experiment?

Answer 30

λ = ax/D
λ = wavelength (m)
a = distance between slits (m)
x = distance between the ‘straight through’ and the 1st bright fringe (m)
D = distance between slits and screen (m)
This equation only applies if a &laquo_space;D keeping θ less than 10^o

Question 31

What is the number of the pattern, n, on either side of the central maximum is known as?

Answer 31

Order

Question 32

What is the diffraction equation?

Answer 32

n λ = d sinθ
n = order of the maximum (no units).
λ = wavelength of light (m).
d = slit separation (m).
θ = angle that the beam makes with the grating (degrees or rads)

Question 33

What is a standing wave?

Answer 33

A wave that has its energy confined to a fixed position

Question 34

What is a node in relation to standing waves?

Answer 34

Nodes are points in a stationary wave at which there is no displacement of the particles at any time

Question 35

What is an anti-node in relation to standing waves?

Answer 35

A point in a standing wave with maximum displacement

Question 36

What conditions must be met to produce a standing wave in a sting or pipe?

Answer 36

The two waves that overlap must be travelling in opposite directions, have the same frequency and have approximately equal amplitudes.

Question 37

What are the standing wave equations for string?

Answer 37

L=1/2λ
L=2/2λ
L=3/2λ
L = length of string
λ = wavelength

Question 38

What are the standing wave equations for a open pipe?

Answer 38

L=1/4λ
L=3/4λ
L = length of string
λ = wavelength

Question 39

What are the standing wave equations for a closed pipe

Answer 39

L=1/2λ
L=λ
L=3/2λ
L = length of string
λ = wavelength