Module 4- Waves

Question 1

What is a progressive wave?

Answer 1

A progressive (moving wave) carries energy from one place to another without transferring any material. The transfer of energy is in the same direction as the wave is travelling.

Question 2

What is the displacement?

Answer 2

How far a point on the wave has moved from its undisturbed points.

Question 3

What is the amplitude?

Answer 3

The maximum magnitude of the displacement

Question 4

What is Wavelength

Answer 4

The length of one whole wave cycle, e.g. from crest to crest or trough to trough.

Question 5

What is the period, T

Answer 5

the time taken for a whole cycle to complete

Question 6

What is the frequency?

Answer 6

The number of cycles (vibrations) per second passing a given point

Question 7

What is the phase?

Answer 7

The measurement of the position of a certain point along the wave cycle.

Question 8

What is the Phase difference

Answer 8

The amount one wave lags behind another

Question 9

What is a transverse wave?

Answer 9

Transverse waves are waves where the vibration is at right angles to the direction of travel.

Question 10

What are longitudinal waves?

Answer 10

In longitudinal waves the vibrations are along the direction of travel.

Question 11

What is intensity?

Answer 11

the intensity of a progressive is the radiant power passing through a surface per unit area.

Question 12

What are the properties all electromagnetic waves have in common?

Answer 12

All EM waves travel in a vacuum at a speed of 300 million m/s
They are transverse waves consisting of vibrating electric and magnetic fields. The electric and magnetic fields are at right angles to each other and to the direction of travel.
They can all polarise

Question 13

What is reflection?

Answer 13

Reflection occurs when a wave changes direction at a boundary between two different media, remaining in the original medium

Question 14

Example of reflection

Answer 14

Light reflecting off a mirrored surface. The light will remain in the original medium (air).

Question 15

What is the law of reflection?

Answer 15

The law of reflection applies whenever waves are reflected.

It states that the angle of incidence is equal to the angle of reflection.

Question 16

What is refraction?

Answer 16

refrcation occur when a wave changes direction as it chages speed when it passes from one medium to another.

Question 17

If a wave speeds up what happens to the refracted ray?

Answer 17

it refracts away from the normal.

Question 18

what is diffraction?

Answer 18

When waves passing through a gap or around an obstacle spread out.

Question 19

what is polarisation?

Answer 19

The phenomenonin which oscillations of a transverse wave are limited to only one phase.

Question 20

what is partial polarisation?

Answer 20

when transverse waves reflect off a surface they become partially. this means there are more waves oscillating in one partciular plane.

Question 21

What is the relationship between intensity and amplitude?

Answer 21

intensity is directly proportional to the sqaure of the amplitude.
when ripples travel across the surface of a bond the intensity drops as the energy is spread out. this causes a drop in the amplitude. decreased amplitude means a reduced average speed of the oscillating particles. halving the amplitude results in particles oscillating with half the speed and a quarter of the kinetic energy.

Question 22

what is the refractive index?

Answer 22

n = c/v

Question 23

what is snells law?

Answer 23

n1sinθ = n2sinθ

Question 24

what is total internal reflection?

Answer 24

when light strikes the boundary at a large angle to the normal, it is totally internally relfected. All the light is reflected back into the original medium.

Question 25

what are the two conditions for total internal reflection?

Answer 25

1. the light must be travelling through a medium with a higher refractive index as it strikes the boundary with a lower refractive index.
2. the angle at which the light strikes the boundary must be above the critical angle.

Question 26

what is the equation to find the critical angle?

Answer 26

nSinC = n(air)sin90

Question 27

What is the principle of superposition of waves?

Answer 27

When two similar types of waves meet at a point the resultant displacement at that point is equal to the sum of the displacements of the individual waves.

Question 28

what is superposition?

Answer 28

the overlaping of two waves at a point in space.

Question 29

What is interference?

Answer 29

superposition of two progressive waves from coherent sources to produce a resultant wave with a displacement equal to the sum of the individual displacements of the 2 waves.

Question 30

what is coherence?

Answer 30

coehrence refers to when waves emitted from two sources having a constant phase difference. In order to be coherent the two waves must have the same frequency.

Question 31

What is path difference?

Answer 31

the difference in the distance travelled by two waves from their sources to a specific point.

Question 32

what is phase difference?

Answer 32

The difference in angle between any points on the same wave or 2 similar points on 2 waves.

Question 33

What is the defintion of monochromatic light?

Answer 33

light of a single frequency.

Question 34

How did young set up his double slit

Answer 34

He used a monochromatic light source and a narrow single slit to diffract the light. light diffracting from the single slit arrives at the double slit in phase. it then diffracts again from the double slit. Each slit acts as a source of coherent waves, which spread from each slit, overlapping and forming an interference pattern that can be seen on a screen as alternating bright and dark regions called fringes.

Question 35

what did young’s double slit expermient show?

Answer 35

it succesfully demonstrated the wave nature of light. young used his experiment to determine the wavelength of various different colours of visible light.

Question 36

What happens when you shine white light through a diffraction grating?

Answer 36

white light is a mixture of colours. as you diffract white light through a grating then the patterns due to different wavelengths within white light are spread out by different amounts.
each orer in the pattern becomes a spectrum, with red on the outside and violet on the inside.

Question 37

how is a stationary wave formed?

Answer 37

superposition of two progressive waves with the same frequency travelling in opposite directions.

Question 38

what are the features of stationary waves?

Answer 38

it remains in a constant position with no net transfer of energy and is characterised by its nodes and anti-nodes.

Question 39

what is node?

Answer 39

a point where the displacements cancel out.

Question 40

what is antinode?

Answer 40

points when two waves are in phase. it is the point with the greatest amplitude and therefore intensity.

Question 41

compare and contrast progressive and stationary waves?

Answer 41

progressive waves - energy transfered in the direction of the wave.
the phase changes across one complete cycle of the wave.
all parts of the wave have the same ampliude.
stationary wave- no net energy transfer.
wavelength is twice the distance between adjacent nodes.
all parts of the wave between a pair of nodes are in phase, and on different sides of a node they are in antiphase.

Question 42

what is the fundamental frequency?

Answer 42

the lowest frequency at which an object can vibbrate

Question 43

how can sound waves form stationary waves?

Answer 43

Sound waves can reflect off a surface to form a stationary wave. The original wave and the reflected wave travel in opposite directions and superpose.

Question 44

approx wavelength for radio waves and microwaves?

Answer 44

radio -10 ^-1m to 10^6m

micro- 10^-3m to 10^-1 m

Question 45

approx wavelength for IR ,visible light and UV?

Answer 45

IR - 7 x 10^-7 m - 10^-3 m
Visible light - 4 x 10^-7m - 7x10^-7m
Ultraviolet - 10^-8 m -4x10^-7

Question 46

approx wavelength for X-rays and gamma rays?

Answer 46

X-rays - 10^-8 m - 10^-13 m

Gamma - 10^-10 m - 10^-16 m

Question 47

describe how a standing wave can be formed on a spring with one fixed end?

Answer 47

• the spring is oscillated at one end.
• the waves travel along the spring are reflected off the fixed end and travel back in the opposite direction.
• as long as minimal energy is absorbed during the reflection, you have 2 waves with the same speed,wavelength and frequency travelling in opposite directions.

Question 48

describe the stationary wave formed with a closed air tube?

Answer 48

-because air is not able to move through the closed end, a node must be formed at this location.

Question 49

describe the stationary wave formed with an open-air tube?

Answer 49

-if the air tube is open at both ends, the air is free to vibrate at both ends which we show as anti-nodes at each end.

Question 50

Describe how stationary waves are formed with microwaves?

Answer 50

• microwaves produce a microwave transmitter
• they are reflected off a metal reflecting plate back towards the transmitter
• the reflected and incoming waves interfere and set up stationary waves
• you can find the nodes and anti nodes by moving the microwave recover between the transmitter and the reflecting plate.
• node will give a minimum reading on the meter value and max value for anti node