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Waves Flashcards

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0
Q

The higher the refractive index of a material the higher its

A

Optical density

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1
Q

The more optically dense a material the more light

A

Slows down when it travels through it.

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2
Q

How is the refractive index of a material, s, calculated?

A

N = refractive index = C / Cs

C = speed

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3
Q

What is the speed of light

A

3 x 10^8 ms^-1

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4
Q

The refractive index of air can be assumed to be … Because …?

A

1 because the speed of light in air is only a very small amount slower than in a vacume.

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5
Q

When light is refracted what stays the same and what changes?

A

It’s speed and wavelength change but its frequency stays the same.

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8
Q

Light bends away from the medium when it moves from a

A

More to less optically dense medium.

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9
Q

Total internal reflection happens when

A

Light going into a less optically dense object is at the critical angle or higher.

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10
Q

Can total internal refraction happen going from a less to more optically dense medium?

A

No, only from more to less.

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11
Q

In an optical fiber what is more optically dense, the core of cladding?

A

The core

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12
Q

Why are optical fibres narrow?

A

So that the light always reflects (It won’t be bellow the critical angle)

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13
Q

What are some of the advantages of using optical fibres for tv and phones rather than electricity?

A

Light has a higher frequency so light can carry more information.
Does not heat up fibre, little energy loss.
No electrical interference
Can travel very quickly

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14
Q

What is the difference between a mechanical and electromagnetic wave?

A

Mechanical waves need a medium to travel through for their propagation while electromagnetic waves do not - they can travel through a vacume.

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15
Q

Examples of mechanical waves are …

A

Water waves
Sound waves
Waves in a string

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16
Q

Step index optical fibres refers to …

A

The step down of the refractive index in stages from the core to the cladding.

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17
Q

Information sent down optical fibres is a …… Signal.

A

Digital

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18
Q

The signal in optic fivers broaden as they travel why could this be a problem?

A

If separate signals broaden and merge together this could reduce the quality.

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19
Q

The digital signal in an optical fibre degrades due to

A

Absorption and scattering from contact with the material in the fiber.

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20
Q

A signal in an optical fiver broadens as it travels because …

A

Light that travels straight down the middle (an axial ray) takes less time than one that bounced of the sides (a non-axial ray)

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21
Q

The principle of superposition states that …

A

When two or more waves cross, the resultant displacement equals he sum of the individual displacements.

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22
Q

Two points on a wave are exactly out of phase if they are …

A

An odd number of half-cycles apart.

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23
Q

To be in phase waves need to have the same what?

A

Frequency and wavelength.

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24
Q

Why is a stationary wave?

A

It is the superposition of two progressive waves with the same frequency (or wavelength) and the same amplitude moving in opposite directions.

25
Q

Is any energy transferred by a stationary wave?

A

No

26
Q

What can be used to make waves on a piece of string?

A

A Oscillator

27
Q

The frequencies at which a wave happens to produce a multiple of half a wavelength an forms a oscillating loop that does not change shape is called?

A

Resonant frequencies

28
Q

What are resonant frequencies?

A

The frequencies at which an exact number of half a wavelength are across the string.

29
Q

An anti node is where amplitude in a standing wave is at its

A

Maximum

30
Q

A node on a standing wave is where the amplitude is at a

A

Minimum

31
Q

At which of these is there constructive or destructive interference?
Node
Antinode

A

Node - destructive

Antinode - constructive

32
Q

Resonant frequents can be named according to their antinodes, how?

A

The Ath harmonic

A = number of antinodes

33
Q

The second harmonic has how many nodes and why is its other name?

A

It has 3 nodes

AKA the first overtone

34
Q

How many wavelengths fit on the third harmonic, how many nodes does it have and what is it also known as!

A

1 1/2 wavelengths
4 nodes
AKA the second overtone

35
Q

As each you progress to the next harmonic what happens to?
Wavelengths that fit on?
Frequency ?
Nodes?

A

Extra 1/2 a wavelength
Frequency increases by one fundamental frequency.
Nodes increase by 1

36
Q

The heavier the string the ….. The fundamental frequency, why?

A

The lower because the wave travels slower. The wavelength is constant and c=f x lander. F decreases.

37
Q

The loser the string the …… the fundamental frequency, why?

A

Lower because the wave is slower.

38
Q

Can microwaves form stationary waves by reflecting I metal?

A

Yes

39
Q

What is diffraction?

A

When light spreads out after passing through a narrow gap.

40
Q

An wave will diffract most when it passes through a gap …

A

That is of a similar size to the waves wavelength

41
Q

To observe a diffraction pattern the light should be

A

Monochromatic (the same frequency)

42
Q

Describe a single slit diffraction pattern.

A

A bright central fringe with alternating dark an bright fringes on ether side of it.

43
Q

What does coherent mean?

A

The frequency and wavelength are the same.

They have a fixed phase difference..

44
Q

For two source interference to take place the waves must be …

A

Monochromatic (one frequency)
Coherent :
Same wavelength, frequency constant phase difference

45
Q

What are advantages of using a laser to demonstrate interference.

A 
Light form a laser is monochromatic 
Light from a laser is coherent. 
Light from a laser is concentrated into a beam. 
Easy to use 
Inexpensive.
46
Q

Laser can be very damaging to eyes. (Burn the retina) what safety precautions can be taken when using a laser?

A 
Never shine at a person 
Wear laser safety goggles 
Avoid shining the laser beam at a reflective surface. 
Have a warning sign. 
Turn the laser of when not needed.
47
Q

What is the criteria for the light interference for
Single source?
Double slit?

A

Single - monochromatic

Double - monochromatic + coherent

48
Q

Any point that is in equal distant from the two sources what will happen? What is it called? (3)

A

The light will be in phase
Constructively interfere
This is called a maxima

49
Q

What will happen at any point where the the path difference is half wavelength e.g 1 1/2 or 4 1/2?
What are these points called?

A

The waves will be out of phase
Total destructive interference occurs
These dark points are called minima.

50
Q

In two source interference? What happens at

Minima and maxima

A

At maxima the light is in phase and constructive interference occurs.
At minima the light is out of phase and destructive interference occurs.

51
Q

In terms of wavelength when do constructive and destructive interference happen. From two slit interference?

A

Constructive when path difference
= n wavelengths

Destructive when path difference
= (n+1/2) wavelengths

52
Q

Why for two source interference of light can’t you have two different sources?

A

The light might not be coherent

By using two slits the light is coherent.

53
Q

How can you work out fringe spacing (w) using
Distance between the slits (D) ?
An slit spacing?

A

W=D wavelength / S

54
Q

What is the equation for frying spacing in double slit interference?

A

W= (D x wavelength) / s

D = distance between source and fringes. 
s = slit spacing.
59
Q

What is the law of refraction between two boundaries n1 and n2?

A

N1sin(@1) = n2sin(@2)

@1 = angle of incidence 
@2 = angle of refraction
60
Q

Light bends towards the normal when travelling from a …

A

Less to more optically dense medium.

Physics (12 decks)

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