Waves

Question 1

what’s a progressive wave

Answer 1

it’s a wave that carries energy from one place to another without transferring any material

Question 2

what’s transverse and longitudinal waves

Answer 2

transverse — oscillate perpendicularly to the direction of energy transfer

ex . EM waves

Longitudinal — oscillate parallel to the direction of energy transfer

Question 3

what waves can’t be polarised

Answer 3

longitudinal

Question 4

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

Answer 4

no light will get through

Question 5

how to tv and radio signals get polarised

Answer 5

there’s TV aerials that’s rods are all horizontal. this is so Tv signals are polarised by the orientation of the rods on the broadcasting aerial.

to receive strong signal, you have to line up rods on the receiving aerial with the rods on the transmitting aerial.

same for radio when you move the aerial around your signal will come and go as the transmitting and receiving aerials go in and out of phase

Question 6

how is it proven that sunlight is made up of transverse waves

Answer 6

the reflected light has been partially polarised

only transverse waves can be polarised

Question 7

explain how polaroid sunglasses help reduce glare caused by reflection

Answer 7

Polaroid material only transmits vibrations in one direction

reflected light mostly vibrates in one direction, so polaroid sunglasses filter that one direction, reducing glare

Question 8

why can sound waves not be polarised

Answer 8

sound in longitudinal wave

vibrations are in same direction as energy transfer so it can’t be polarised

Question 9

what is superposition

Answer 9

when two or more waves pass through each other

Question 10

what’s the principle of superposition

Answer 10

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

Question 11

what’s interference

Answer 11

when two or more waves interfere
either destructive or constructive

trough and trough = bigger trough
trough and crest = zero

for destructive interference to be noticeable the opposing amplitudes need to be nearly equal

Question 12

waves that are in phase have what in common

Answer 12

same displacement
same velocity

it means when the waves are at the same point in the wave cycle
or in sync

Question 13

what’s the angles of phase and not in phase

Answer 13

in phase
0 or 360

out of phase
odd number multiples of 180
180

Question 14

what does it mean to be coherent

Answer 14

two sources have to have
same wavelength
same frequency
fixed phase difference

Question 15

what’s the formula for constructive interference and destructive interference path difference

Answer 15

constructive
path diff = n x wavelengths

destructive
path diff = ( n + 0.5 ) x wavelength

Question 16

why is it hard to observe interference patterns in areas affected by two waves that are coherent

Answer 16

interference only is noticeable if amplitudes of the two waves are approximately equal

Question 17

what’s a stationary wave

Answer 17

is the superposition of two progressive waves with the same frequency, moving in opposite directions

no energy is transmitted by a stationary wave

Question 18

how do you detect stationary wave

Answer 18

setting up a driving oscillator at one end of a stretched string with the other end fixed. the wave generated by the oscillator will be reflected back and forth

Question 19

what are nodes and antinodes

Answer 19

nodes are when amplitudes of the vibration is zero.

antinodes are points of maximum amplitude

Question 20

what’s the first harmonic

Answer 20

it’s when the waves vibrates at the lowest possible resonant frequency
2 nodes and one antinodes

Question 21

how can you demonstrate stationary waves with microwaves and sound

Answer 21

microwaves reflects off a metal plate making stationary waves

stationary sound waves are produced in the glass tube
the lycopodium powder laid along the bottom of the tube is shaken away

Question 22

what’s a progressive wave

Answer 22

it’s a wave that carries energy from one place to another without transferring any material

Question 23

what does the length, weight, and tension of string do to the resonant frequency experiment

Answer 23

( more l) the longer the string, the lower the resonant frequency

(more mu) the heavier the string, the lower the resonant frequency

(less tension) the losses the string the lower the resonant frequency because waves travel more slowly down a loose string

Question 24

how does the diffraction differ when the gap is bigger or smaller or the same than wavelength

Answer 24

when gap is a lot bigger than wavelength, diffraction is UNNOTICEABLE

the most diffraction you could get is when a gap is the same size as the wavelength

if gap is smaller then part of the wave is reflected back

Question 25

what happens when white light is diffracted

Answer 25

the wavelengths of the diff colours diffract diff amounts so the centre point will be white and the rest will be a spectra of colours with violet being the closest to the centre and red being the furthest

Question 26

what does an increase of intensity mean in monochromatic light

Answer 26

it means an increase in the number of photons per second

Question 27

how does the width of the central maximum vary with the wavelength and slit size ijcreasing slit width and wavelength

Answer 27

increasing slit width decreases amount of diffraction. so central max is narrower and intensity is stronger increasing wavelength increases the amount of diffraction. so central max is wider and has a less intensity

Question 28

what’s a refractive index

Answer 28

RI of a material is the measure of how much it slows down light

Question 29

why does light go faster in a vacuum

Answer 29

cuz it doesn’t collide with any particles

Question 30

what’s the critical angle

Answer 30

it’s the angle when the refraction is on the boundarie or 90 degrees

Question 31

what’s TIR

Answer 31

it’s when the angle of incidence is more than critical angle which causes total reflection

Question 32

why does an optical fibre use cladding

Answer 32

its used as it has a lower refractive index than the optical fibre. this allows TIR and it prevents scratches which could let light escape

Question 33

how does the TIR work in optical fibre and who is fibre narrow

Answer 33

the light is shine at one end and fibre is narrow so the light always hits the boundary between fibre and cladding at a bigger angle than the critical angle which causes TIR so it hits the next boundary until it reaches the end of the fibre

Question 34

what causes signal degradation

Answer 34

Absorption Dispersion

Question 35

explain absorption and how to fix it

Answer 35

as signal travels some of the energy is lost through absorption by the material of the fibre l. this energy loss results in the amplitude of the signal to be reduced use a optical fibre repeater

Question 36

explains eh two types of dispersion and how to prevent it

Answer 36

MODAL — light rays enter fibre at diff angles, so it takes diff paths. which causes the data to be scrambled use a single mode fibre and optical fibre repeater MATERIAL — some wavelengths travel faster than others so you use monochromatic light to stop it both lead to pulse broadening and they can overlap confusing the signal also use optical fibre repeater