11 - Waves 1

Question 1

Define progressive wave.

Answer 1

An oscillation that transfers energy but doesn’t transfer matter.

Question 2

Define mechanical wave.

Answer 2

Progressive waves that require a medium to travel through.

Question 3

Define electromagnetic wave.

Answer 3

Progressive wave that can travel through a vacuum.

Question 4

How do mechanical waves move?

Answer 4

.Movement of matter transfers energy.
.Particles move from equilibrium position to new position as the wave travels through the medium.
.This requires a force which they exert on their neighbours like springs.

Question 5

Define transverse wave.

Answer 5

Energy transported perpendicular to the direction of oscillation.

Question 6

Define longitudinal wave.

Answer 6

Energy transported parallel to the direction of oscillation.

Question 7

What are the movements of a longitudinal wave called?

Answer 7

Compression and rarefaction.

Question 8

What are some examples of longitudinal waves?

Answer 8

.Sound waves.
.P-waves.
.Pressure waves.

Question 9

What are some examples of transverse waves?

Answer 9

.EM waves.
.Water waves.

Question 10

Define amplitude.

Answer 10

The maximum displacement from the equilibrium position (m).

Question 11

Define wavelength.

Answer 11

The maximum distance between two points in phase on adjacent waves (m).

Question 12

Define frequency.

Answer 12

The number of waves passing a point per unit time (Hz/s^-1).

Question 13

Define time period.

Answer 13

The time taken for a wave to move past a given point/time taken for one oscillation (s).

Question 14

How are time period and frequency related?

Answer 14

Inversely proportional - f = 1/T

Question 15

Define displacement.

Answer 15

Distance travelled in a specific direction.

Question 16

What is the wave speed equation?

Answer 16

v = fλ.

Question 17

What speed do EM waves through a vacuum travel at?

Answer 17

3 x 10^8 ms^-1.

Question 18

What is another equation for wave speed?

Answer 18

v = λ/T.

Question 19

Define phase difference.

Answer 19

The difference between different displacements along a wave/difference in displacements of different waves.

Question 20

How do you measure phase difference?

Answer 20

As they are oscillations - in angles in radians.

Question 21

Define in phase.

Answer 21

When a part continually has the same displacement - either 0 or 2pi radians.

Question 22

Define antiphase.

Answer 22

When a part continually has the opposite displacement.

Question 23

How do you work out phase difference in degrees?

Answer 23

= x/λ x 360.

Question 24

Define ray.

Answer 24

Representation of a wave - straight line with an arrow indicating energy transport direction.

Question 25

Define reflection.

Answer 25

When a wave changes direction at a boundary between two materials.

Question 26

Define refraction.

Answer 26

When a wave changes direction and speed when passing from one material to another.

Question 27

What are the laws of reflection?

Answer 27

.Angle of incidence = angle of reflection. .Wavelength and frequency don't change. .Reflected wave gains additional 90 degrees phase difference from the incident wave.

Question 28

What happens in refraction?

Answer 28

.Changes velocity. .If bends towards normal, slows down. .If bends away, speed increases. .When wave slows down - wavelength decreases but frequency is constant.

Question 29

Why do waves slow when wavelength decreases?

Answer 29

.E = hv/λ. .λ = hv/e .So they are directly proportional when E is constant.

Question 30

What acronym helps with refraction?

Answer 30

Fast. Away. Slow. Towards.

Question 31

What is diffraction?

Answer 31

.When waves spread out after passing through a gap. .Done by all waves. .Speed, wavelength and frequency don't change. .Only direction changes.

Question 32

What does the magnitude of diffraction depend on?

Answer 32

.Wave wavelength. .Gap size. The more comparable they are, the larger the magnitude of diffraction e.g. light/sound with a door.

Question 33

Define plane polarised waves.

Answer 33

Waves which oscillate in one plane.

Question 34

Define unpolarised waves.

Answer 34

waves oscillating in many possible planes e.g. filament lamp light.

Question 35

Explain why longitudinal waves can't be plane polarised.

Answer 35

.Energy transport is parallel to oscillations. .All oscillations are limited to one plane. .Therefore, can't be plane polarised.

Question 36

What happens to reflected transverse waves?

Answer 36

.Become partially polarised - more waves oscillating in one plane but not fully. .Sunglasses - block out reflected partially polarised light but not unpolarised light.

Question 37

How do polarisers work with EM waves?

Answer 37

.Vertical polarisers allow vertically aligned fields pass through. Vice versa with horizontal polarisers. MICROWAVES ARE THE EXCEPTION AND BEHAVE IN THE OPPOSITE WAY DUE TO ELECTRON MOVEMENT.

Question 38

What are some uses of polarisers.

Answer 38

.Communication polarisers - reduce interference. .3D cinema glasses.

Question 39

What experiment shows polarisation?

Answer 39

.Take 2 filters and light and the light measuring thingy. .Rotate 1 filter. .Measure again and repeat. .Should produce cosine wave looking pattern but above x-axis.

Question 40

Define intensity.

Answer 40

The radiant power through a surface with unit area.

Question 41

What are the intensity equations and units?

Answer 41

I = P/A I = P/4pir^2 I = Wm^-2.

Question 42

What is the relationship between intensity and amplitude?

Answer 42

Intensity is proportional to Amplitude^2.

Question 43

What is refractive index?

Answer 43

.n = c/v .No units.

Question 44

What is the refractive index in air?

Answer 44

n = 1.0003.

Question 45

Why is n always greater than or equal to one.

Answer 45

The velocity must always be less than the speed of light as waves can't travel faster than c in a vacuum.

Question 46

What are the conditions for Total Internal Reflection?

Answer 46

.Light must be travelling through a medium with a higher n and hits a boundary of a material with a lower n. .The angle at which the light strikes the boundary must be above the critical angle which depends on the material's n.

Question 47

What happens when the angle is below/equal to/above the critical angle?

Answer 47

.Some reflected/refracted. .Sent along the boundary. .TIR.

Question 48

What are the equations for TIR?

Answer 48

sin0c = 1/n1 or n1 = 1/sin0c.

Question 49

How does fibre optics work?

Answer 49

.Light travels down due to TIR. .Used in communication and medical endoscopes.

Question 50

How does cladding work?

Answer 50

.Reduces light loss by giving a 2nd chance at TIR. .Increases critical angle but faster if only travels through the core. .If it has a lower n than the core, TIR occurs. .If it has a higher n, refraction occurs.

Question 51

LOOK IN FOLDER FOR CLADDING GRAPH DIAGRAM THINGY.