Refraction Diffraction And Interference

Question 1

what is path difference

Answer 1

is the difference in the distance travelled by two waves

Question 2

what is a coherent light source

Answer 2

has the same frequency and wavelength and a fixed phase difference

Question 3

what is an example of a coherent and monochromatic light

Answer 3

lasers as they emit a single wavelength of light

Question 4

what does the youngs double slit experiment demonstrate

Answer 4

interference of light from two sources

Question 5

what do you do in the youngs double slit experiment

Answer 5

she a coherent light source through two slits about the same size as the wavelength of the laser light so the light diffracts
each slit acts as a coherent point source making a pattern of light and dark fringes

Question 6

how are the bright spots formed in youngs double slits

Answer 6

constructive interference takes place as they are in phase which also mean the path difference in (n)lambda

Question 7

What is the equation associated with youngs double slits

Answer 7

Fringe spacing = (wavelength x distance between screen and slits)/slit separation

Question 8

What happens if you use a white light instead of a laser in youngs double slit experiment

Answer 8

White light gives a wider maxima and a less intense diffraction pattern with a central white fringe with alternation bright fringes which are spectra

Question 9

Which wavelength diffracts the least and the most

Answer 9

Least - violet
Most - red

Question 10

What are the safety precautions needed while using a laser

Answer 10

Wear laser safety goggles
Don’t shine laser at reflective surfaces
Display a warning sign
Never shine the laser at someone

Question 11

How was the evidence of the wave nature of light provided by youngs double slit experiment

Answer 11

Because diffraction and interference are wave properties and so proved that EM radiation must act as a wave

Question 12

What was the other theory of what light was made out of apart from waves

Answer 12

Formed from tiny Particles

Question 13

What is diffraction

Answer 13

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

Question 14

When does the greatest diffraction occur

Answer 14

When the gap is the same size or close to the same size as the wavelength

Question 15

What happened if the gap is smaller than the wavelength or larger than the wavelength

Answer 15

Smaller - most waves are reflected
Bigger - less noticeable diffraction as when a wave meets an obstacle you get diffraction around the edges the wider the obstacle compared to the wavelength the less diffraction occurs

Question 16

What type of light can be diffracted through a single slit onto a screen

Answer 16

Monochromatic light

Question 17

When a monochromatic light is shined through a single slit onto a screen what interference pattern forms

Answer 17

The pattern is made up of light and dark fringes it has a bright central fringe which is double the width of all the other fringes with alternating dark and bright fringes on either side the intensity of the fringes decreases from the central fringe

Question 18

What are the bright and dark fringes caused by

Answer 18

Bright - caused by constructive interference where the waves meet in phase
Dark - caused by destructive interference where the waves meet out if phase

Question 19

How does the diffraction pattern look different when using white light instead of a monochromatic light

Answer 19

As white light is made up of all colours the colours have different wavelengths so diffract at different amounts so you get a spectrum of the colours instead of one colour from a single wavelength

Question 20

how can you change the width of the central maximum

Answer 20

you can change slit width and wavelength

Question 21

what does increasing the slit width do to the amount of diffraction and what happens to the central maximum

Answer 21

it decreases the amount of diffraction so the central maximum becomes narrower and its intensity increases

Question 22

what does increasing the wavelength do to the amount of diffraction and happens to the central maximum

Answer 22

it increases the amount of diffraction and as the slit is closer in size to the lights wavelength the central maximum becomes wider and its intensity decreases

Question 23

what is a diffraction grating

Answer 23

is a slide containing many equally spaced slits very close together

Question 24

when a monochromatic light passes through a diffraction grating what happens to the interference pattern and why does that happen

Answer 24

it becomes more sharper and brighter than it would be if passed through a youngs double slit this is because there are many more light rays reinforcing the pattern

Question 25

what is the ray passing through the centre of the diffraction grating called

Answer 25

0th order

Question 26

what is the formula associated with diffraction gratings

Answer 26

distance between slits x sin(angle) = order x wavelength

Question 27

when wavelengths increases what happens to the distance between the orders

Answer 27

the distance between the orders will increase because the angle is larger due to an increase in diffraction as the slit spacing is closer to the size of the wavelength

Question 28

what is the maximum value of sin(angle)

Answer 28

1 so 90 degrees

Question 29

what is the path difference between each order

Answer 29

n lambda when n is a whole number

Question 30

what do you get when you split up light from a star using a diffraction grating and what does it show

Answer 30

a line absorption spectra which can be used to show which elements are present in a star

Question 31

wat is a refractive index

Answer 31

is a property of a material which measures how much it slows down light passing through it

Question 32

how do you calculate refractive index

Answer 32

refractive index = speed of light in a vacuum / the speed of light in a substance

Question 33

a material with a higher refractive index can also be known as what

Answer 33

being more optically dense

Question 34

What happens when a wave enters a different medium

Answer 34

It refracts causing it to change direction either towards or away depending on the materials refractive index

Question 35

What causes the direction of the wave to change in a different medium

Answer 35

The speed of the wave changes causing it to change direction

Question 36

If the object is more optically dense does the ray refract towards or away from the normal

Answer 36

Towards as it slows down

Question 37

As the angle of incidence increases what other angle increases

Answer 37

The angle of refraction

Question 38

When does the angle of incidence reach the critical angle

Answer 38

When the angle of refraction is exactly 90 degrees and the light is refracted along the boundary

Question 39

When can total internal reflection occur

Answer 39

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

Question 40

What is useful application of total internal reflection

Answer 40

Optical fibres

Question 41

What are optical fibres

Answer 41

They are flexible, thin tubes of plastic or glass which carry information in the form of light signals

Question 42

What is the structure of an optical fibre

Answer 42

They have an optically dense core surrounded by cladding

Question 43

What does the cladding do to the optical fibre

Answer 43

It has a lower optical density allowing TIR to occur and also protects the core from damage and prevent signal degradation through light escaping the core which can cause information to be lost

Question 44

What are the two things that cause signal degradation

Answer 44

Absorption and dispersion

Question 45

How does absorption cause signal degradation

Answer 45

A part of the signals energy is absorbed by the fibre reducing the amplitude of the signal which could lead to loss of information

Question 46

How does dispersion cause signal degradation

Answer 46

It cause pulse broadening which is where the received signal is broader than the original transmitted signal and these broadened signals can overlap causing loss of information

Question 47

What are the two types of dispersion

Answer 47

Modal and material

Question 48

What is modal dispersion

Answer 48

Caused by light rays entering the fibre at different angles therefore they take different paths along the fibre this leads to the rays taking a different amount of time to travel along the fibre causing pulse broadening

Question 49

How can modal dispersion be reduced

Answer 49

By making the core very narrow therefore making the possible difference is path length smaller

Question 50

What is material dispersion

Answer 50

Caused by light consisting of different wavelengths meaning rays will travel at different speeds along the fibre which leads to pulse broadening

Question 51

How can material dispersion be prevented

Answer 51

By using a monochromatic light

Question 52

What can both absorption and dispersion be reduced by

Answer 52

Using an optical fibre repeater which regenerates the signal during it travel to its destination