11 - Waves

Question 1

What do waves transfer?

Answer 1

energy and information

Question 2

How can you class waves?

Answer 2

mechanical or electromagnetic

Question 3

Define a progressive wave

Answer 3

A wave that transfers energy from one place to another without a transfer of matter between the two points. The two progressive wave types are longitudinal and transverse waves.

Question 4

What waves require a medium to travel through?

Answer 4

Mechanical waves require a medium, longitudinal waves require a medium and so can’t travel in vacuums.

Question 5

What is a transverse wave?

Answer 5

A wave where the direction of oscillation is perpendicular to the direction of energy transfer of the wave. They have peaks and troughs at maximum displacement from the equilibrium position

Question 6

Example of transverse waves

Answer 6

light waves, springs (slinkys), s waves, water waves, waves on a string

Question 7

What is a longitudinal wave?

Answer 7

A wave where the direction of oscillation is parallel to the direction of energy transfer of the wave

Question 8

Examples of longitudinal wave

Answer 8

sound waves, p waves

Question 9

What is wave displacement?

Answer 9

distance from equilibrium position in metres

Question 10

What is amplitude?

Answer 10

maximum displacement from equilibrium position in metres

Question 11

What is wavelength?

Answer 11

length of one complete oscillation (distance between two same points of a wave)

Question 12

What is time period?

Answer 12

the time taken for one full oscillation to happen in seconds

Question 13

What is frequency?

Answer 13

the number of wavelengths that pass a certain point in one second measured in Hz

Question 14

What is wavespeed?

Answer 14

The distance travelled by a wave per unit time measured in m/s

Question 15

time period, freq equation

Answer 15

P=1/T

Question 16

What is a wave profile?

Answer 16

A graph showing the displacement of particles in the wave against the distance along the wave. It can be used to determine the wavelength and amplitude of both types of wave. The displacement of the particles in the wave is continuously changing so the wave profile changes shape over time

Question 17

What can be determined from a wave’s displacement against time graph?

Answer 17

time period and amplitude of both types of wave

Question 18

Wavespeed equation

Answer 18

v=fλ
velocity = frequency x wavelength

Question 19

What is phase difference?

Answer 19

the difference between the displacement of the particles along a wave or the difference between the displacements of the particles on different waves.

Question 20

What is phase difference measured in?

Answer 20

degrees or radians (2pi radians = 360degrees)

Question 21

Phase difference equation

Answer 21

Ф= (x/λ) x 360°
Ф= (x/λ) x 2pi

Question 22

What is a wavefront?

Answer 22

a line joining points on a wave, which are in phase

Question 23

When does reflection occur?

Answer 23

When a wave changes direction at a boundary between two different mediums, remaining in the original medium, e.g. a mirrored surface.

Question 24

What is the law of reflection?

Answer 24

The angle of incidence is equal to the angle of reflection when measured to the normal

Question 25

Change in wave properties during reflection

Answer 25

frequency and wavelength of wave remain unchanged

Question 26

When does refraction occur?

Answer 26

When a wave changes direction as it changes speed when it passes from one medium to another. The amount of refraction depends on the refractive index of the material

Question 27

Change in wave properties during refraction

Answer 27

wavelength changes but frequency remains unchanged

Question 28

Refraction - entering medium with higher optical density

Answer 28

Wave slows down, wavelength decreases, bends towards normal

Question 29

Refraction - entering medium with lower optical density

Answer 29

wave speeds up, wavelength increases, bends away from normal

Question 30

What is the refractive index equal to?

Answer 30

the speed of light in vacuum / the speed of light in material

or sini/sinr

Question 31

greater refractive index…

Answer 31

the more the light entering the medium is refracted towards the normal

Question 32

refractive index (n) equation

Answer 32

n=c/v
refractive index = 3x10^8 / speed in medium

Question 33

What is diffraction?

Answer 33

The spreading out of a wave as it passes through a gap/aperture or when it encounters an obstacle

Question 34

Change in wave properties in diffraction?

Answer 34

speed, wavelength and frequency remain unchanged

Question 35

Conditions for diffraction

Answer 35

Diffraction will only occur if the wavelength of the wave is of a similar size to the size of aperture. Diffraction effects are more significant when the wavelength is a similar size to the gap

Question 36

What is polarisation?

Answer 36

The particles oscillate along one direction only, confined to a single plane

Question 37

polarised v unpolarised light

Answer 37

Unpolarised light is light which oscillates in many different planes wheres polarised light is light which oscillates in one plane only

Question 38

Why can’t longitudinal waves be polarised?

Answer 38

The direction of oscillations are already in the same direction that the wave travels in (already acts on single plane) so only transverse waves can be polarised

Question 39

What is total internal reflection?

Answer 39

When all light is reflected back into the original medium and no refraction occurs

Question 40

Conditions for TIR

Answer 40

original material must have higher refractive index than surrounding material (e.g. glass to air), angle of incidence must be greater than the critical angle

Question 41

What is the critical angle?

Answer 41

The critical angle is the angle of incidence above which the total internal reflection occurs, the angle of incidence where the angle of refraction is 90°

Question 42

critical angle equation

Answer 42

sinc =1/n

Question 43

TIR equation

Answer 43

n1sinϑ1=n2sinϑ2