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As Physics > Section 2 (waves) > Flashcards

Section 2 (waves) Flashcards

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1
Q 
Define the following:
Amplitude
Frequency
Wavelength
Phase difference
A

Amplitude- distance from 0 to crest/ trough
Frequency- the number of cycles per second (Hz)
Wavelength- the length of one complete wave
Phase difference- the difference between two identical except points

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2
Q

What is the equation for calculating frequency?

A

f=1/T

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3
Q

What equation is used to calculate wave speed?

A

c=f,\

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4
Q

All ___ waves travel at the same speed when ___ _ ___.

A

All electromagnetic waves travel at the same speed when in a vacuum.

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5
Q

Describe transverse waves.

A

Vibrations go up and down. The displacement of particles are at right angles to the direction of transfer.

Graph:
Displacement|-♈️-> Distance or T
                           ,\ or T
   |||
||    ||    ||
         |||
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6
Q

Describe longitudinal waves.

A

The displacement of particles are the same direction as the energy transfer.

| | ||| | | |

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7
Q

Give some examples of transverse waves.

A

Electromagnetic waves and waves on a string.

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8
Q

Give some examples of longitudinal waves.

A

Sound waves

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9
Q

What is polarisation?

What happens if you have two polarising filters, one of which rotating through 360•?

A

The passing of a wave through the filter, only allowing the vibrations though in one direction.
At 90• and 270• the filters will be perpendicular to one another so minimum light will get through. At 180• and 360• the filters will be aligned to the light will be at maxima.

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10
Q

What is superposition of waves?

A

When two or more waves pass through each other.
If two crests/ troughs meet there will be constructive interference.
If a crest and a trough meet there will be destructive interference.

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11
Q

What are the two ways that phase difference may be measured as?

A

As angles in degrees or radians or as fractions of a cycle.

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12
Q

How are stationary waves formed?

A

By two waves of the same frequency travelling in opposite directions meeting to create a node.

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13
Q

What is the first harmonic?

A

It is where one ‘loop’ is made from stationary waves with a nodes at each end. The wavelength would be double the length of the string.

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14
Q

Give two examples of stationary waves.

A

Microwaves (reflecting a microwave beam at a metal plate, the meter would receive no signal at nodes and maximum signal at antinodes) and sound waves (powder laid along a glass tube attached to the speaker gathers at the nodes).

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15
Q

Waves cause the ___ of the medium they travel through to ___.

A

Waves cause the particles of the medium they travel through to oscillate.

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16
Q

Describe the diffraction of white light.

A

White light is made up of different colours with different wavelengths. They all diffract by different amounts. Red has the shortest wavelength so would diffract the most, violet the least.

17
Q

Name a source of monochromatic light and the diffraction pattern it would cause.

A

Lasers are a source of monochromatic light. The centre fringe on the screen would be the brightest, the light intensity decreasing on the other fringes.
/\
^^’ ‘^^

18
Q

How does the width of the central maximum vary with the width of the slit and wavelength of light being diffracted?

A

Increasing the slit width decreases the amount of diffraction. Therefore the central maximum is narrower and the intensity is higher.
Increasing the wavelength increases the amount of diffraction. Therefore the central maximum is wider and the intensity is lower.

19
Q

What is coherence?

A

Two waves have the same wavelength and frequency and a fixed phase difference between them. The troughs and crests line up causing constructive interference.

20
Q

What is path difference?

A

The amount by which the path travelled by one wave is longer than the path travelled by the other wave is called the path difference.

21
Q

Explain the patterns seen during two-source interference.

A

As you move the probe/ microphone parallel to the microwave generator/ speakers, you’ll get an alternating pattern of strong (maxima) and weak (minima) signals.

22
Q

What is young’s double slit formula?

A 
w=,\D
       s
w- fringe spacing (m)
,\- wavelength (m)
D- distance between slits and screen (m)
s- distance between slits
23
Q

What is the advantage to using a diffraction grating through which light is directed?

A

The fringes are sharper

24
Q

What is the diffraction grating equation?

A

dsin🚫=n,\
d-distance between slits (m)
🚫- angle to the normal made by the maximum
n- order of maximum (how many from central fringe)
,- wavelength (m)

25
Q

What are applications for diffraction gratings?

A

To see line (absorption) spectra.

X-Ray crystallography (found the structure of DNA).

26
Q

What is the absolute refractive index?

What is the relative refractive index between two materials?

A

Absolute refractive index- the ratio between the speed of light in a vacuum and in the material.
Relative refractive index-the ratio of the speed of light in material 1 to material 2.

27
Q

What is the approximate refractive index of air?

A

1

28
Q

What is Snell’s law of refraction and the equation that goes with it?

A

Of light is passing through a boundary between two materials, you can use the law of refraction to calculate unknown angles of refractive indices.

n1sin🚫1= n2sin🚫2
n-refractive index

29
Q

What is the critical angle?

What is the equation?

A

Where the light refracted away from the normal is 90•.

sin🚫c=n2/n1

🚫c- critical angle
n- refractive index

30
Q

What is total internal reflection?

A

Where the angle of incidence are greater than the critical angle and the light is reflected back.

31
Q

Describe step-index optical fibres.

A

They have a high refractive index core surrounded by cladding with a lower refractive index to allow total internal reflection.
The cladding also protects the fibre from scratches.

32
Q

What are the advantages to using optical fibres?

A 
There is no electrical interference.
No energy lost as heat.
Signal can carry more information.
Fibre-optic cables are cheaper to produce.
The signal can travel further, quicker.
33
Q

Optical fibres can degrade. What is absorption and dispersion?

A

Absorption- some of the signals energy is absorbed by the material in the fibre.
Dispersion- cause pulse broadening
-> modal dispersion- light rays may enter at the wrong angle so take a longer path. Reduced by using a single mode fibre.
-> material dispersion- different amounts of refraction experienced by different wavelengths. Using monochromatic light can reduce this.

As Physics (4 decks)

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