Waves

Question 1

Mechanical waves

Answer 1

waves that require a medium

Question 2

progressive wave

Answer 2

transfers energy in the direction of propergation

Question 3

longitudinal waves

Answer 3

oscillates parallel to the direction of energy propagation

Question 4

transverse waves

Answer 4

oscillations that are parallel to the direction of energy propagation

Question 5

compressions

Answer 5

high pressure areas

Question 6

rarefractions

Answer 6

low pressure areas

Question 7

how does a person hear music from speakers across a room?

Answer 7

• vibrations from the speaker cause particles around the speaker to oscillate
• these oscillations are passed to neighbouring particles and so on across the room until the particles in the persons ear are vibrating
  *this causes the person to hear a sound

Question 8

wavelength

Answer 8

the length of a single wave cycle

Question 9

frequency

Answer 9

the number of wave cycles passing a point each second

Question 10

what happens if amplitude increases with frequency and speed remaining the same?

Answer 10

more energy transferred per second

Question 11

what happens when freqency increases with amplitude and speed remaining the same?

Answer 11

more energy transferred per second

Question 12

what will an oscillating charged particle generate?

Answer 12

• an electric field perpendicular to the magnetic field
• a megnetic field perpendicular to an electric field

– therefore an electromagnetic wave

Question 13

polarisation

Answer 13

when oscillations of a transverse wave are limited to one plane / direction

Question 14

what happens when a wave is polarised?

Answer 14

• intensity decreases
• energy decreases

Question 15

refractive index of air

Answer 15

1

Question 16

what happends when a wave travels through a substance with a higher refractive index?

Answer 16

• speed decreases
• wavelength decreases

Question 17

what happens when light hits the boundry at a right angle?

Answer 17

light will remain in a straight line

Question 18

normal

Answer 18

a line perpendicular to the boundry between substances

Question 19

angle of incidence

Answer 19

the angle the wave enters the boundry

Question 20

angle of refraction

Answer 20

the angle the wave exits the boundry

Question 21

refraction

Answer 21

when a wave changes direction as it crosses a boundry

Question 22

snells law

Answer 22

n1sinx1=n2sinx2

Question 23

monochromatic light

Answer 23

waves that have one colour, wavelength and frequency

Question 24

critical angle

Answer 24

the angle of incidence which total internal reflection occurs

Question 25

what is the condition for the refracive index for TIR to occur?

Answer 25

the wave must move from a higher refractive index to a lower n1>n2

Question 26

optical fibres

Answer 26

transports infomation using TIR

Question 27

core (optical fibre)

Answer 27

* provides a medium for TIR * allows signal to travel

Question 28

cladding (optical fibre)

Answer 28

* has a lower refractive intex than the core so TIR can occur * protects the core by keeping info secure and prevent it from escaping

Question 29

why does pulse absorption occur?

Answer 29

a pulse may arrive to the optical fibre with a much lower amplitude than it began with

Question 30

what may be wrong with an optical fibre for pullse absorption to occur?

Answer 30

* imperfections in cladding or core * impurities in core

Question 31

what is pulse broadening

Answer 31

a pulse looses its rectangular shape as it travels due to light taking longer than it should to reach the end

Question 32

what is modal (multipath) dispersion?

Answer 32

* laser light taking different journeys of different lengths to reach the end of the fibre * can cause pulse broadening

Question 33

how can modal (multipath) dispersion be improved?

Answer 33

* making sure pulse only travels short distances *use a monomode fibre since they have thin cores, which limits laser light to a single path

Question 34

what is material dispersion?

Answer 34

* occurs when we send signals down the optical fibres with a range of different wavelengths, which travel at different speeds * causes pulse broadening

Question 35

how can material dispersion be reduced?

Answer 35

* using monochromatic light * using repeters

Question 36

what do repeters do

Answer 36

* takes the signal part-way through the journey then retransmitts it

Question 37

diffraction

Answer 37

when waves pass through a gap or hit an obstical they spread out

Question 38

superposition

Answer 38

when two waves meet and add together at a point

Question 39

path length

Answer 39

the distance a wave travels from its source to a given point

Question 40

path difference

Answer 40

the difference between two paths --> can only be measures if the waves have the same wavelength

Question 41

constructive interference

Answer 41

when the peaks of two waves align perfectly so the amplitude of the resultant wave is at a maximum (nλ)

Question 42

destructive interference

Answer 42

when the peak of one wave aligns with the trough of another so the amplitude of the resultant wave is at a minimum (n+1/2)λ

Question 43

in phase

Answer 43

when the peaks of two superposed waves line up perfectly

Question 44

out of phase

Answer 44

when the peaks of two superposed waves do not line up perfectly

Question 45

what is the path difference of an in phase wave?

Answer 45

even multiples of pi

Question 46

what is the path difference of an out of phase wave?

Answer 46

odd multiples of pi

Question 47

property of light be to have a stable pattern in doube slit experiment

Answer 47

a constant phase difference

Question 48

constant phase difference

Answer 48

light from each slit having the same wavelength and frequencu

Question 49

property of light to have a distinctive pattern in doube slit experiment

Answer 49

coherene

Question 50

coherence

Answer 50

constant phase differnce and same frequency

Question 51

how can coherence be ensured?

Answer 51

* add colour filter to decrease range of frequncies so we can treat light as having the same wavelength * add single slit between filter and double slit since it behaves as a single source of light

Question 52

fringe spacing (w)

Answer 52

distance between two adjacenct maxima or minima

Question 53

describe the pattern when using white light in double slit experiment

Answer 53

* one central white fringe * rainbow fringes on either side that progress from blue to red as we move outward from the centre

Question 54

single slit diffraction pattern

Answer 54

* central fringe which has a greater width than the other bright fringes

Question 55

describe the double slit patterm in comparision to double slit pattern

Answer 55

* more distinct fringes * more fringes * thinner fringes