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Physics > Refraction Diffraction And Interference > Flashcards

Refraction Diffraction And Interference Flashcards

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1
Q

what is path difference

A

is the difference in the distance travelled by two waves

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2
Q

what is a coherent light source

A

has the same frequency and wavelength and a fixed phase difference

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3
Q

what is an example of a coherent and monochromatic light

A

lasers as they emit a single wavelength of light

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4
Q

what does the youngs double slit experiment demonstrate

A

interference of light from two sources

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5
Q

what do you do in the youngs double slit experiment

A

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

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6
Q

how are the bright spots formed in youngs double slits

A

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

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7
Q

What is the equation associated with youngs double slits

A

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

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8
Q

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

A

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

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9
Q

Which wavelength diffracts the least and the most

A

Least - violet
Most - red

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10
Q

What are the safety precautions needed while using a laser

A

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

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11
Q

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

A

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

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12
Q

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

A

Formed from tiny Particles

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13
Q

What is diffraction

A

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

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14
Q

When does the greatest diffraction occur

A

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

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15
Q

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

A

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

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16
Q

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

A

Monochromatic light

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17
Q

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

A

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

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18
Q

What are the bright and dark fringes caused by

A

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

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19
Q

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

A

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

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20
Q

how can you change the width of the central maximum

A

you can change slit width and wavelength

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21
Q

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

A

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

22
Q

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

A

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

23
Q

what is a diffraction grating

A

is a slide containing many equally spaced slits very close together

24
Q

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

A

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

25
Q

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

A

0th order

26
Q

what is the formula associated with diffraction gratings

A

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

27
Q

when wavelengths increases what happens to the distance between the orders

A

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

28
Q

what is the maximum value of sin(angle)

A

1 so 90 degrees

29
Q

what is the path difference between each order

A

n lambda when n is a whole number

30
Q

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

A

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

31
Q

wat is a refractive index

A

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

32
Q

how do you calculate refractive index

A

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

33
Q

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

A

being more optically dense

34
Q

What happens when a wave enters a different medium

A

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

35
Q

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

A

The speed of the wave changes causing it to change direction

36
Q

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

A

Towards as it slows down

37
Q

As the angle of incidence increases what other angle increases

A

The angle of refraction

38
Q

When does the angle of incidence reach the critical angle

A

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

39
Q

When can total internal reflection occur

A

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

40
Q

What is useful application of total internal reflection

A

Optical fibres

41
Q

What are optical fibres

A

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

42
Q

What is the structure of an optical fibre

A

They have an optically dense core surrounded by cladding

43
Q

What does the cladding do to the optical fibre

A

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

44
Q

What are the two things that cause signal degradation

A

Absorption and dispersion

45
Q

How does absorption cause signal degradation

A

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

46
Q

How does dispersion cause signal degradation

A

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

47
Q

What are the two types of dispersion

A

Modal and material

48
Q

What is modal dispersion

A

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

49
Q

How can modal dispersion be reduced

A

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

50
Q

What is material dispersion

A

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

51
Q

How can material dispersion be prevented

A

By using a monochromatic light

52
Q

What can both absorption and dispersion be reduced by

A

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

Physics (18 decks)

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