section 2: waves and optics

Question 1

what are mechanical waves + 3 examples

Answer 1

waves that pass through a substance.
sound, seismic, wave on a string.

Question 2

define longitudinal wave

Answer 2

wave which direction of vibration is parallel to the direction of the wave. Has areas of compression and rarefaction.

Question 3

define transverse wave

Answer 3

wave which direction of vibration is perpendicular to the direction of the wave.

Question 4

are mechanical waves perpendicular or longitudinal

Answer 4

perpendicular

Question 5

whats a polarised wave

Answer 5

a wave that only vibrates on 1 plane

Question 6

how to stop light passing through polaroids or slits.

Answer 6

light travels through 1st polaroid and becomes polarised.
light travels through 2nd polaroid which is turned 90 degrees to the 1st. no light gets through.

Question 7

define: displacement, amplitude, wavelength, period, frequency

Answer 7

displacement - distance and direction from equilibrium.
amplitude - maximum displacement. trough to peak.
wavelength - distance between 2 adjacent peaks.
period - time for 1 wave to pass a fixed point.
frequency - waves passing a point per second.

Question 8

whats phase difference

Answer 8

fraction of a cycle between the vibrations of 2 particles.

Question 9

what are waves in a ripple tank called.
at what direction does the wave travel to them

Answer 9

wavefronts
right angles

Question 10

when does rarefaction occur

Answer 10

when waves pass across a boundary at which wave speed and wavelength changes.

Question 11

why does rarefaction occur in glass

Answer 11

wave moves slower in glass than air.

Question 12

how does the size of a diffraction grating affect how much the waves spread

Answer 12

bigger gap = less spread

Question 13

whats superposition

Answer 13

when 2 waves meet, they combine

Question 14

what is created when 2 crests or 2 troughs meet

Answer 14

crests = supercrest created
trough = supertrough created

Question 15

what happens to amplitude when a crest meets a trough of the same amplitude

Answer 15

it is 0

Question 16

what are nodes and antinode

Answer 16

node - point of no displacement on a stationary wave
antinode - point of maximum displacement on a stationary wave

Question 17

in terms of wavelength, whats the distance between 2 nodes

Answer 17

1/2 wavelength

Question 18

how many nodes does the 1st, 2nd and 3rd harmonics have

Answer 18

1 - 2
2 - 3
3 - 4

Question 19

at what frequencies are stationary waves formed

Answer 19

f, 2f, 3f…

Question 20

how to change pitch with tension

Answer 20

increase tension or shortening length = higher pitch.
decrease tension or increase length = lower pitch

Question 21

in the equation f = 1/2l root T/μ, what does every letter mean

Answer 21

f = frequency
l = length
T = tension
μ = linear density (mass/kg)

Question 22

what way to the normal will light bend when moving in and out of glass

Answer 22

in to glass - bend towards normal
out of glass - away from normal

Question 23

equation for refractive index of a substance. what do letters mean

Answer 23

n = sini/sinr
n is refractive index
i is angle from wave line to normal entering box.
r is angle from normal to line in the box

Question 24

in equation n = c/cs, what do letters mean

Answer 24

n = refractive index
c = wave speed
cs = wave speed in substance

Question 25

in equation n1sinΘ1 = n2sinΘ2 , what do letters mean

Answer 25

n1 = refractive index of substance 1 Θ1 = angle to the normal going in n2 = refractive index of substance 2 Θ2 = angle to the normal going out

Question 26

when will total internal reflection take place

Answer 26

the angle of incidence is greater than the critical angle. and the incident substance has a greater refractive index than the other substance.

Question 27

what are optical fibres used in

Answer 27

endoscopes - to see inside the body

Question 28

what makes up an optical fibre

Answer 28

a core surrounded by cladding of lower refractive index to reduce light loss from the core.

Question 29

where does total internal reflection take place in an optical fibre

Answer 29

the core-cladding boundary.

Question 30

why is it important an optical fibre core is narrow

Answer 30

to prevent modal dispersion

Question 31

whats modal dispersion

Answer 31

the lengthening of a light pulse in an optical fibre, due to rays that undergo less total internal refraction

Question 32

explain double split experiment

Answer 32

laser shone through double slits. this means the waves are coherent. dark and light fringes formed on screen

Question 33

what does a bright fringe mean in double slit experiment

Answer 33

light waves are in phase

Question 34

what does a darkfringe mean in double slit experiment

Answer 34

light waves are 180 degrees out of phases

Question 35

in equation w = λD/s , whats w, D and s

Answer 35

W is fringe separation D is distance from slits to screen s is slit spacing

Question 36

what makes 2 waves coherent

Answer 36

if they emit waves with constant phase difference

Question 37

what does large fringe spacing mean about λ

Answer 37

high

Question 38

what would need to be used before the double slit if the light source wasnt coherent

Answer 38

a single slit

Question 39

describe what is seen on the screen in single slit diffracation (3)

Answer 39

central fringe is twice as wide than the rest. peak intensity decreases as you go away from centre. each of the outer fringes is the same width.

Question 40

whats a diffraction grating

Answer 40

plate with many close slits

Question 41

what happens when light passes through a diffraction grating

Answer 41

passes through each slit and is diffracted. creates orders where light goes. 0 order in middle, then 1st, 2nd...

Question 42

2 ways angle of diffraction is increased in a diffraction grating

Answer 42

slits closer. higher λ

Question 43

in dsinΘ = nλ , what does each letter mean

Answer 43

d = grating spacing Θ = angle from order 0 to slit to an order n is order number

Question 44

3 types of spectra and explain

Answer 44

continuous - measures temp of light source as the hotter the source, the shorter the wavelength. Line emission - coloured lines produced from a chemical produced in the light. Line absorption - continuous with dark lines superimposed on the continuous spectrum. due to elements.