optics

Question 1

what is the equation of refractive index?

Answer 1

sin incidence/ sin refraction

Question 2

what does coherent mean?

Answer 2

there is a constant phase difference

Question 3

what does monochromatic mean?

Answer 3

the light wave contains only one wavelength of light

Question 4

what is the effect of a greater wavelength of light on single slit interference

Answer 4

-the fringes are wider

Question 5

what is the effect of a narrower slit on single slit interference

Answer 5

-the fringes are wider

Question 6

where does total internal reflection occur in optical fibres

Answer 6

at the core cladding boundary

Question 7

why does total internal reflection occur in fibres

Answer 7

to prevent the light reaching the wrong direction as the signals would not be secure

Question 8

why is the core narrow on an optical fibre

Answer 8

to prevent modal dispersion so the first pulse of light doesn’t merge with the second pulse

Question 9

name the two requirements for light sources to be coherent

Answer 9

same wavelength

constant phase difference

Question 10

when does refraction not occur

Answer 10

if the incident light ray is along the normal

Question 11

at a boundary between two transparent substances how does a light ray bend

Answer 11

towards the normal if going into a more dense substance

away from the normal if going into less dense substance

Question 12

state three advantages of an optical fibre having a smaller core

Answer 12

• less light is lost
• better signal quality
• less change of angle between each reflection

Question 13

state an application of optical fibres

Answer 13

communications

Question 14

when will total internal reflection occur

Answer 14

if the incident substane has a larger refractive index than the other substanece
if the ange of incidence exceeds the critical angle

Question 15

what is modal dispersion

Answer 15

lengthening of light waves
due to undergoing repeaditly total internal reflection having to travel longer distance than light rays that undergo fewer internal reflections

Question 16

what happens to a signal in an optical fibre when it undergoes absorbance

Answer 16

part of signals energy absorbed by fibre

reduces amplitude of signal

Question 17

what is a material dispersion

Answer 17

light rays will travel at different speeds across the fibre this can lead to pulse broadening

Question 18

what is pulse broadening

Answer 18

where the received signal is broader

than the original transmitted signal

Question 19

how do you prevent modal dispersion

Answer 19

making the core very narrow

so difference in path lengths smaller

Question 20

how are the fringes formed in a double slit experiment

Answer 20

due to interference of light

Question 21

what occurs at bright fringes in double slit experiment

Answer 21

light waves from each slit arrive in phase with each other so light from each slit reinforces each other

Question 22

what occurs at dark fringes in double slit experiment

Answer 22

light waves from the two slits arrive 180 degrees out of phase so light from one slight cancels out light from the other

Question 23

what is a coherent source of light

Answer 23

one which emits waves of same frequency with constant phase difference

Question 24

describe white light fringe from a single slit

Answer 24

central fringe is white
inner fringe blue inner side red outer side
outer fringes merge into white light getting fainter with bigger distance from centre

Question 25

how will diffracted waves spread out more

Answer 25

gap is narrower

wavelength is larger

Question 26

outline a single slit diffraction pattern

Answer 26

central fringe twice as wide as outer fringes
peak intensity of each fringe decreases with increasing distance from centre
each outer fringe same width
outer fringes less intense than central fringe