waves

Question 1

what are some applications of polarisation?

Answer 1

polaroid sunglasses
TV and radio signals

Question 2

what happens when two waves meet and have equal but opposite displacements?

Answer 2

destructive interference

Question 3

what is superposition?

Answer 3

where the displacements of two waves are combined as they pass each other

Question 4

when does constructive interference occur?

Answer 4

when two waves have displacement in the same direction

Question 5

when is a stationary wave formed?

Answer 5

formed from the superposition of 2 progressive waves,
travelling in opposite direction in the same plane,
with the same frequency, wavelength and amplitude

Question 6

is energy transferred by a stationary wave?

Answer 6

no

Question 7

what is another name for the lowest frequency at which stationary waves form?

Answer 7

the first harmonic

Question 8

what is the distance between adjacent nodes (or antinodes)

Answer 8

half a wavelength

Question 9

what is path difference?

Answer 9

the difference in the distance travelled by two waves
the difference in distances travelled from two coherent sources to an interference fringe

Question 10

what are 3 properties of a coherent light source?

Answer 10

it has the same frequency and wavelength
and a fixed phase difference

Question 11

why are lasers used in diffraction experiments

Answer 11

they form clear interference patterns

Question 12

are lasers coherent?

Answer 12

yes

Question 13

what are some safety precations when using lasers

Answer 13

wear laser safety goggles
don’t shine the laser at reflective surfaces
display a warning sign
never shine lasers at a person

Question 14

what does Young’s double slit experiment provide evidence for?

Answer 14

wave nature of light

Question 15

what does diffraction and interference of light provide evidence for?

Answer 15

wave nature of light

Question 16

what is diffracion?

Answer 16

the spreading out of waves when they pass through or around a gap

Question 17

what would be observed if white light was diffracted

Answer 17

a spectrum of colour in the diffraction pattern

Question 18

which colour is furthest from the central white maximum in the diffraction of white light

Answer 18

red

Question 19

which colour is closest to the central white maximum in the diffraction of white light

Answer 19

violet

Question 20

What can be varied to change the width of the central diffraction maximum?

Answer 20

slit width and wavelength

Question 21

what is a diffraction grating?

Answer 21

a slide containing many equally spaced slits very close together

Question 22

when can total internal reflection (TIR) occur?

Answer 22

when the angle of incidence is greater than the critical angle and the incident refractive index is greater than the refractive index of the material at the boundary

Question 23

name an application of TIR

Answer 23

optical fibres

Question 24

describe the optical densities of parts of an optical fibre

Answer 24

optically dense core
surrounded by a less optically dense claddding

Question 25

What is useful about the cladding in optic fibres

Answer 25

allows TIR to occur
protects core from damage
prevents signal degradation / information loss (through light escaping the core)

Question 26

what is phase difference?
what is it measured in?

Answer 26

in radians,
for two objects oscillating in the same time period, T p.d. = 2pi Δt /T
delta t is the time between successive instants when the two objects are at maximum displacement in the same direction

Question 27

what is a node?

Answer 27

a fixed point in a stationary wave pattern where the amplitude is zero

Question 28

what is modal dispersion?

Answer 28

the lengthening of a light pulse as it travels along an optical fibre, due to rays that undergo less total internal reflection

Question 29

what is defined as ‘the lengthening of a light pulse as it travels along an optical fibre’?

Answer 29

modal dispersion