waves

Question 1

what is a wave

Answer 1

an oscillation of particles or fields

Question 2

what is a progressive wave

Answer 2

A progressive (moving) wave carries energy from one place to another without transferring any material.

Question 3

what is a cycle of a wave

Answer 3

one complete vibration of the wave

Question 4

what is wavelength

Answer 4

Wavelength, l, metres — the length of one whole wave cycle, from crest to crest or trough to trough.

Question 5

what is the time period of a wave

Answer 5

Period, T, seconds — the time taken for a whole cycle (vibration) to complete, or to pass a given point.

Question 6

what is the frequency of a wave

Answer 6

Frequency, f, hertz — the number of cycles (vibrations) per second passing a given point.

Question 7

what is the phase of the wave

Answer 7

Phase — a measurement of the position of a certain point along the wave cycle.

Question 8

what is the phase difference of a wave

Answer 8

Phase difference — the amount one wave lags behind another.

Question 9

what is reflection of a wave

Answer 9

Reflection — the wave is bounced back when it hits a boundary

Question 10

what Is refraction a wave

Answer 10

Refraction — the wave changes direction as it enters a different medium. The change in direction is a result of the wave slowing down or speeding up.

Question 11

frequency equation

Answer 11

f = 1/ T

Question 12

how to work out the wave speed

Answer 12

wave speed = distance travelled/ time taken

Question 13

how to work out speed of a wave

Answer 13

speed of wave = wavelength x frequency

Question 14

what is the speed of a em wave in a vacuum

Answer 14

c = 3.00 × 108 ms–1

Question 15

what are transverse waves

Answer 15

waves with vibrations perpendicular to the direction of energy transfer.

Question 16

give an example of a transverse wave

Answer 16

em waves

Question 17

what are longitudinal waves

Answer 17

waves with oscillations parallel to the energy transfer

Question 18

give an example of a longitudinal wave

Answer 18

sound waves

Question 19

what is polarisation

Answer 19

when vibrations are restricted to one plane

Question 20

what waves can you polarise

Answer 20

transverse waves

Question 21

what is evidence that electromagnetic waves are transverse

Answer 21

polarisation

Question 22

how can you polarise waves

Answer 22

using a polarising filter

Question 23

if you have two polarising filters at right angles to each other what happens

Answer 23

no light will get through

Question 24

how do polaroid glasses work

Answer 24

Polaroid sunglasses reduce the glare of light reflected by water or glass. The reflected light is polarised and the intensity is reduced when it passes through the polaroid sunglasses.

Question 25

why are the rods on a tv aerial horizontal

Answer 25

TV signals are polarised by the orientation of the rods on the broadcasting aerial. To receive a strong signal, you have to line up the rods on the receiving aerial with the rods on the transmitting aerial — if they aren’t aligned, the signal strength will be lower.

Question 26

what is superposition

Answer 26

the instant the waves cross, the displacements due to each wave combine. Then each wave moves on

Question 27

what is the principle of superposition

Answer 27

when two or more waves cross the resultant displacement equals the vector sum of the individual displacements

Question 28

a crest pus a crest and a trough plus a trough is a example of what

Answer 28

constructive interference

Question 29

a crest plus a trough is an example of what

Answer 29

destructive interference

Question 30

for interference to be noticeable what should be true about the amplitudes

Answer 30

the amplitudes should be nearly equal

Question 31

what does it mean if two points are in phase

Answer 31

if they are both at the same point in the wave cycle

Question 32

what is true about the points displacement and velocity if the points are in phase

Answer 32

same displacement and velocity

Question 33

what angle should you use to show 1 complete cycle of a wave

Answer 33

360 or 2 pi

Question 34

how do you know two points are in phase

Answer 34

the have a phase difference of zero or a multiple of 360

Question 35

how do you know two points are exactly out of phase

Answer 35

have phase difference of odd number multiples of 180

Question 36

how can you get a clear interference pattern

Answer 36

the two or more sources must be coherent and be in phase

Question 37

what does it mean to be coherent

Answer 37

to have the same wavelength and frequency and a fixed phase difference between them

Question 38

what does getting a constructive or destructive interference at a point depend on

Answer 38

how much further one wave travelled that the other wave to get to that point

Question 39

what is path difference

Answer 39

The difference in distance travelled by two waves from their sources to the point where they meet

Question 40

when will you get constructive interference

Answer 40

At any point an equal distance from two sources that are coherent and in phase or where the path difference is a whole number of wavelengths.

Question 41

where do you get destructive interference

Answer 41

But at points where the path difference is half a wavelength, one and a half wavelengths, two and a half wavelengths etc., the waves arrive out of phase and you get destructive interference.

Question 42

when do you get constructive interference (equation)

Answer 42

path difference = nλ

Question 43

where do you get destructive interference (equation)

Answer 43

path difference + (2n + 1)λ /2

Question 44

what is a stationary wave

Answer 44

superposition of two progressive waves with the same frequency (wavelength), moving in opposite directions.

Question 45

what happens with stationary waves that doesn't happen with progressive waves

Answer 45

no energy is transmitted

Question 46

what are nodes

Answer 46

where amplitude is zero

Question 47

what are antinodes

Answer 47

points of maximum amplitude

Question 48

what is diffraction

Answer 48

the way waves spread out as they come through a narrow gap or go around obstacles

Question 49

what does the amount of diffraction depend on

Answer 49

depends on the wavelength of the wave compared to the size of the gap

Question 50

what happens to the diffraction when the gap is a lot bigger than the wavelength

Answer 50

diffraction is unnoticeable

Question 51

what happens to diffraction when you have a gap several wavelengths wide

Answer 51

you get noticeable diffraction

Question 52

what happens to diffraction when the size of the gap is roughly the same size as the wavelength

Answer 52

you get the most diffraction

Question 53

what happens to diffraction if the size of the gap is smaller than the wavelength

Answer 53

no diffraction an the waves are mostly reflected back

Question 54

to get a clear diffraction pattern for light what do you need to do

Answer 54

use a monochromatic coherent light source

Question 55

what does monochromatic mean

Answer 55

the light has all the same wavelength so its the same colour

Question 56

what is an example of a monochromatic coherent light source

Answer 56

lasers

Question 57

what happens you shine light through a narrow slit

Answer 57

you get a diffraction pattern that has a central bright fringe with dark and bright fringes alternating on either side where the bright and dark fringes are created by destructive and constructive interference

Question 58

what happens when you diffract white light through narrow slit

Answer 58

you get a diffraction pattern of a central bright white fringe where the fringes are a spectra of colours with blue on the inner side and red on the outer side and fringes getting fainter the further you move outwards

Question 59

why do you get that specific diffraction pattern for white light when shone through a narrow slit

Answer 59

because white light is a mixture of colours each with different wavelengths so when diffracted all the wavelengths are diffracted by different amounts

Question 60

what happens to central maximum if you decrease slit width

Answer 60

you decrease the amount of diffraction and so the central maximum is narrower and the intensity of the central maximum is higher