Definitions 3

Question 1

Progressive waves

Answer 1

Waves that transfer energy, but not matter, as a result of oscillations or vibrations through a medium or vacuum

Question 2

Transverse waves

Answer 2

Waves in which the particles oscillate perpendicular to the direction of motion and energy transfer

Question 3

Longitudinal waves

Answer 3

Waves in which the particles oscillate parallel to the direction of motion and energy transfer

Question 4

Frequency

Answer 4

The number of oscillations of a wave per unit time

Question 5

Period

Answer 5

The time taken for one complete oscillation of a wave

Question 6

Amplitude

Answer 6

The maximum distance of a particle in a wave from its equilibrium or rest position

Question 7

Displacement

Answer 7

The distance of a point on a wave from its rest or equilibrium position

Question 8

Phase difference

Answer 8

The difference in positions of two points on a single wave or between two waves of the same frequency or how much a point or a wave is in front or behind another

Question 9

Intensity

Answer 9

The power per unit area or the energy passing through a unit area per unit time

Question 10

Doppler effect

Answer 10

The change in observed frequency when a source of sound waves moves relative to a stationary observer

Question 11

Electromagnetic waves

Answer 11

Transverse waves that travel at the speed of light through a vacuum

Question 12

Polarisation

Answer 12

The restriction of the oscillations of the particles in a transverse wave to only one direction

Question 13

What are the properties of standing waves?

Answer 13

1. They are formed from waves of the same frequency, amplitude and wavelength travelling in opposite directions
2. They consist of nodes and antinodes that are fixed - the peaks and troughs do not move
3. They do not transfer energy
4. All points between two adjacent nodes oscillate in phase
5. All points in adjacent loops oscillate in anti-phase

Question 14

Wavelength

Answer 14

The distance between two points in phase with each other on consecutive oscillations of a wave

Question 15

What happens when the time-base unit or voltage unit on a cathode-ray oscilloscope turns off?

Answer 15

1. If the time-base unit is turned off you will see a straight vertical line on the screen
2. If the voltage unit is turned off you will see a straight horizontal line on the screen

Question 16

What is the relationship between the frequency and wavelength of a wave?

Answer 16

For a wave at constant speed, λ ∝ 1 / f, so when λ increases, f decreases and vice versa

Question 17

State the relationships between the intensity, amplitude and frequency of a wave?

Answer 17

1. I ∝ A^2
2. I ∝ f^2

Hence, if A or f is doubled, I increases by a factor of 4 or 2^2

Question 18

What is the relationship between the intensity and distance of a spherical wave?

Answer 18

The area of a spherical wave passes through the surface area of a sphere, so A = 4πr^2, hence:

I = P / 4πr^2

If no energy is absorbed, we get:

I ∝ 1 / r^2

As you move farther from the source the same energy gets spread over a larger area, so the intensity of the spherical wave decreases rapidly

Question 19

Why can’t longitudinal waves be polarised?

Answer 19

The particles of a longitudinal wave oscillate parallel to the direction of energy transfer, which means they are already moving one direction

Question 20

When occurs when unpolarised light meets a polariser?

Answer 20

The intensity of the unpolarised light will decrease be 1/2 when it moves through the polariser

Question 21

What occurs if the polariser and analyser have the same orientation?

Answer 21

If they have the same orientation, the transmission axes of both filters are 0° or 180° to each other, which means that the incident light will have the same intensity as the transmitted light, since cos(0° or 180°) = 1

Question 22

What if the polariser and analyser are at right angles?

Answer 22

If they are at right angles, the transmission axes of both filters are 90° or 270° to each other, and so as cos(90° or 270°) = 1, the intensity of the transmitted by the analyser will be zero

Question 23

State the equation for polarisation:

Answer 23

I = Io * cos^2(θ)

θ = the angle between the direction of the incident light and the transmission axis of the polariser

Question 24

What is the formula for the length of a stationary wave that is fixed at both ends?

Answer 24

L = nλ / 2

n = all positive integers

Question 25

What is the formula for the length of a stationary wave that is open at one end?

Answer 25

L = nλ / 4 n = only odd positive integers

Question 26

Why do stationary waves that are open at one end only have odd harmonics?

Answer 26

There is always a node at the closed end of the stationary wave and an antinode at the open end, which causes only odd multiples of 1/4λ to be added to each successive harmonic

Question 27

What is the formula for the length of a stationary wave that is open at both ends?

Answer 27

L = nλ / 2 n = all positive integers

Question 28

What happens to a wave when it is diffracted?

Answer 28

The amplitude decreases, but all other properties remain the same

Question 29

Path difference

Answer 29

The difference in distance one wave has to travel compared to another to reach the same point

Question 30

How do you calculate the path difference for constructive interference?

Answer 30

Constructive interference = nλ n = the maxima you are looking to calculate (0...5)

Question 31

How do you calculate the path difference for deconstructive interference?

Answer 31

Deconstructive interference = (n +1/2)λ n = the minima you are looking to calculate (0...5)

Question 32

Diffraction grating

Answer 32

A diffraction grating is a plate on which there is a very large number of closely-spaced, identical slits so that when monochromatic light is incident on it, a pattern of narrow bright fringes is produced

Question 33

How do you calculate the angle between a maxima and the central maxima?

Answer 33

θ = tan-1(h / D) h = n * x - distance between maxima D = distance between slits to screen

Question 34

What do bright fringes look like?

Answer 34

They are bright bands of light that are evenly spaced out and their intensity decreases from either side of the central bright fringe

Question 35

How do you identify areas of compression and rarefaction on a displacement time graph?

Answer 35

Areas of compression and rarefaction always appear when x = 0

Question 35

How do you identify an area of compression?

Answer 35

If the displacements above and below the point are coming towards each other, the point is an area of compression

Question 36

How do you identify an area of rarefaction?

Answer 36

If the displacements above and below the point are moving away from each other, the point is an area of rarefaction

Question 37

List the conditions for superposition:

Answer 37

1. The waves must be of the same type - both transverse or longitudinal 2. The waves must be coherent - have the same frequency and constant phase difference 3. The amplitude only needs to be the same on both waves to form a stationary wave

Question 38

Monochromatic

Answer 38

Light of a single wavelength

Question 39

How do you calculate phase difference?

Answer 39

For the phase difference between two points on the same wave: 1. Phase difference = 360° * ( x/λ ), where x = the difference in distance between the two points For the phase difference between two points on two difference waves of the same frequency: 1. Phase difference = 360° * ( t/T ), where t = the difference in time between the two points

Question 40

What is a cathode-ray oscilloscope?

Answer 40

An instrument that displays a voltage against time graph for an electric circuit

Question 41

Derive the equation v = fλ:

Answer 41

1. The speed of a wave is given by s = d/t 2. A wave travels one wavelength on one period, hence, v = λ/T 3. If you substitute f = 1/T, the equation becomes v = fλ

Question 42

How do you calculate the intensity of a wave?

Answer 42

I = P/A Where, A is the area perpendicular to the energy transfer of the wave

Question 43

What are the properties of transverse waves?

Answer 43

1. They have crests and troughs 2. They can travel through a vacuum 3. They can be polarised

Question 44

What are the properties of longitudinal waves?

Answer 44

1. They have areas of rarefactions and compressions 2. They cannot travel through a vacuum 3. They cannot be polarised

Question 45

What are areas of rarefaction and compression?

Answer 45

1. A rarefaction is an area of low pressure, with the particles being further apart from each other 2. A compression is an area of high pressure, with the particles being closer to each other

Question 46

What happens when a source of sound waves moves closer to an observer?

Answer 46

The wavelength of the sound waves shorten and compress, which therefore increases the observed frequency for the observer

Question 47

What happens when a source of sound waves moves away from an observer?

Answer 47

The wavelength of the sound waves broaden, which therefore decreases the observed frequency for the observer

Question 48

State the equation for the Doppler effect:

Answer 48

fo = fs [ v / ( v ± vs ) ] v = 340ms^-1

Question 49

What is the relationship between the frequency and energy of an EM wave?

Answer 49

The higher the frequency, the more energy that an EM wave possess, making more ionising, which can lead to cancer

Question 50

Superposition

Answer 50

When two or more waves arrive at the same point and overlap, their amplitudes combine

Question 51

The principle of superposition

Answer 51

When two or more waves overlap at a point, the displacement at that point is equal to the sum of the displacements of the individual waves

Question 52

Stationary waves

Answer 52

Stationary waves are produced by the superposition of two waves of the same frequency, amplitude and wavelength travelling in opposite directions

Question 53

Nodes

Answer 53

Nodes are where there is no vibration, they are always fixed

Question 54

Antinodes

Answer 54

Antinodes are where the vibrations are at their maximum amplitude, they only move in the vertical direction

Question 55

How do you change the harmonic of a stationary wave?

Answer 55

Increasing the frequency increases the wavelength and the number of nodes and antinodes present, while decreasing the frequency does the opposite

Question 56

What is diffraction affected by? DONT UNDERSTAND

Answer 56

Diffraction is dependent on the width of the gap compared to the wavelength of the waves: 1. For gaps that are much smaller than the wavelength, no diffraction occurs 2. For gaps that are much bigger than the wavelength, no diffraction occurs When the wavelength of the wave and the width of the gap are similar in size, then diffraction occurs: 4. When the wavelength is bigger than the gap, more diffraction occurs 5. When the wavelength is smaller than the gap, less diffraction occurs Diffraction is the most prominent when the width of the slit is approximately equal to the wavelength

Question 57

Inteference

Answer 57

Interference, which results from the principle of superposition, occurs when waves overlap and their resultant displacement is the sum of the displacements of each wave

Question 58

Constructive and deconstructive interference

Answer 58

1. Constructive interference occurs when the overlapping waves are in phase, producing a resultant wave that has double the amplitude 2. Deconstructive interference occurs when the overlapping waves are in anti-phase, resulting in a resultant wave that has no amplitude

Question 59

Coherence

Answer 59

Two or more waves are coherent with each other if they have the same frequency and constant phase difference

Question 60

What are the two types of interference fringes?

Answer 60

1. Bright fringes are an indication of an area of constructive interference 2. Dark fringes are an indication of an area of deconstructive interference

Question 61

What are the requirements for two source interference?

Answer 61

1. The sources must be coherent 2. The sources must be monochromatic

Question 62

Describe the setup of Young's double slit experiment:

Answer 62

1. There may be two sources, which are made to interfere with each other 2. There may be a single source, which is made to pass through two small slits

Question 63

What is Young's double slit equation?

Answer 63

λ = ax / D a = distance between the centres of the slits in m x = distance between two adjacent maxima or minima in m D = distance between the slits and the screen in m

Question 64

What is the diffraction grating equation?

Answer 64

dsin(0) = nλ d = distance between two adjacent slits in m θ = angular separation between the order of maxima in ° n = order of maxima (0...5)

Question 65

What is represented by N in diffraction gratings?

Answer 65

N is the number of lines per mm,m or cm: d = 1 / N

Question 66

Where is the maximum angle of diffraction?

Answer 66

The maximum angle of diffraction occurs when θ = 90° and hence, sin θ = 1

Question 67

How do you find the highest order of maxima?

Answer 67

The highest order of maxima is given by n = d / λ, when θ = 90° and hence, sin θ = 1, since n must be a positive integer, if the value obtained is a decimal it must be rounded down