Waves

Question 0

The higher the refractive index of a material the higher its

Answer 0

Optical density

Question 1

The more optically dense a material the more light

Answer 1

Slows down when it travels through it.

Question 2

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

Answer 2

N = refractive index = C / Cs

C = speed

Question 3

What is the speed of light

Answer 3

3 x 10^8 ms^-1

Question 4

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

Answer 4

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

Question 5

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

Answer 5

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

Question 8

Light bends away from the medium when it moves from a

Answer 8

More to less optically dense medium.

Question 9

Total internal reflection happens when

Answer 9

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

Question 10

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

Answer 10

No, only from more to less.

Question 11

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

Answer 11

The core

Question 12

Why are optical fibres narrow?

Answer 12

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

Question 13

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

Answer 13

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

Question 14

What is the difference between a mechanical and electromagnetic wave?

Answer 14

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

Question 15

Examples of mechanical waves are …

Answer 15

Water waves
Sound waves
Waves in a string

Question 16

Step index optical fibres refers to …

Answer 16

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

Question 17

Information sent down optical fibres is a …… Signal.

Answer 17

Digital

Question 18

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

Answer 18

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

Question 19

The digital signal in an optical fibre degrades due to

Answer 19

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

Question 20

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

Answer 20

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

Question 21

The principle of superposition states that …

Answer 21

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

Question 22

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

Answer 22

An odd number of half-cycles apart.

Question 23

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

Answer 23

Frequency and wavelength.

Question 24

Why is a stationary wave?

Answer 24

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

Question 25

Is any energy transferred by a stationary wave?

Answer 25

No

Question 26

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

Answer 26

A Oscillator

Question 27

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?

Answer 27

Resonant frequencies

Question 28

What are resonant frequencies?

Answer 28

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

Question 29

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

Answer 29

Maximum

Question 30

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

Answer 30

Minimum

Question 31

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

Answer 31

Node - destructive | Antinode - constructive

Question 32

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

Answer 32

The Ath harmonic A = number of antinodes

Question 33

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

Answer 33

It has 3 nodes | AKA the first overtone

Question 34

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

Answer 34

1 1/2 wavelengths 4 nodes AKA the second overtone

Question 35

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

Answer 35

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

Question 36

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

Answer 36

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

Question 37

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

Answer 37

Lower because the wave is slower.

Question 38

Can microwaves form stationary waves by reflecting I metal?

Answer 38

Yes

Question 39

What is diffraction?

Answer 39

When light spreads out after passing through a narrow gap.

Question 40

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

Answer 40

That is of a similar size to the waves wavelength

Question 41

To observe a diffraction pattern the light should be

Answer 41

Monochromatic (the same frequency)

Question 42

Describe a single slit diffraction pattern.

Answer 42

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

Question 43

What does coherent mean?

Answer 43

The frequency and wavelength are the same. | They have a fixed phase difference..

Question 44

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

Answer 44

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

Question 45

What are advantages of using a laser to demonstrate interference.

Answer 45

``` 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. ```

Question 46

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

Answer 46

``` 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. ```

Question 47

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

Answer 47

Single - monochromatic | Double - monochromatic + coherent

Question 48

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

Answer 48

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

Question 49

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?

Answer 49

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

Question 50

In two source interference? What happens at | Minima and maxima

Answer 50

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

Question 51

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

Answer 51

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

Question 52

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

Answer 52

The light might not be coherent | By using two slits the light is coherent.

Question 53

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

Answer 53

W=D wavelength / S

Question 54

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

Answer 54

W= (D x wavelength) / s ``` D = distance between source and fringes. s = slit spacing. ```

Question 59

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

Answer 59

N1sin(@1) = n2sin(@2) ``` @1 = angle of incidence @2 = angle of refraction ```

Question 60

Light bends towards the normal when travelling from a ...

Answer 60

Less to more optically dense medium.