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Physics > Topic 11 - Wave phenomena > Flashcards

Topic 11 - Wave phenomena Flashcards

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1
Q

What is the nature of standing (stationary) waves?

A
  • An oscillating wave pattern that does not change its position
  • At nodes, the displacement is always zero
  • At antinodes, the amplitude is at its maximum
  • Between the nodes the oscillations are all in phase
  • Energy is not transferred by a standing wave
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2
Q

How are standing waves formed?

A
  • Caused by interference
  • The overall displacement is the sum of the two individual displacements at that moment
  • Nodes occur where the two waves are always out of phase
  • Antinodes occur where the two waves are perfectly in phase
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3
Q

What is the fundamental mode of vibration (first harmonic)?

A

Vibration where the wavelength is 2L (L = the length of the string)

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4
Q

What is the fundamental frequency, f0, of a string?

A
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5
Q

What are the wavelengths and corresponding frequencies of the harmonics?

A
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6
Q

Describe the modes of vibration on a stretched string

A
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7
Q

What is the fundamental wavelength of a pipe with open ends, closed ends, and one open and one closed end?

A

Both ends open = 2L

Both ends closed = 2L

One open one closed = 4L

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8
Q

Compare standing waves and travelling waves

A
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9
Q

What is meant by the Doppler effect?

A

The change of frequency that is detected when there is relative motion between a source and a receiver of waves.

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10
Q

What kind of waves can show Doppler effect?

A

Any kind

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11
Q

Describe the shape of wavefronts during Doppler effect

A
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12
Q

What is the equation for Doppler effect for sound for a moving source?

A

f’ = frequency received

us = speed of the source

v = the speed of the wave

+ if moving away from the observer

  • if moving towards the observer
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13
Q

What is the equation for Doppler effect for sound for a moving observer?

A

f’ = frequency received

u0 = speed of the observer

v = the speed of the wave

+ if moving towards from the observer

  • if moving away the observer
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14
Q

What is the equation for Doppler effect for electromagnetic waves?

A

v = speed between the source and the observer

Can be used if v << c

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15
Q

How can Doppler effect be used to measure speed?

A
  • Radars and microwaves
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16
Q

Sketch the variation with angle of diffraction of the relative intensity of light diffracted at a single slit

A
17
Q

How is the formula θ = λ/b for the position of the first minimum of the diffraction pattern produced at a single slit derived?

A

θ = λ/b → the angle for the first minimum of a single slit diffraction pattern

18
Q

Sketch the variation with angle of diffraction by two point sources that has been diffracted at a single slit (resolution)

A
  1. Two sources easily resolved
  2. Two sources just resolved
  3. Two sources not resolved
19
Q

What is the Rayleigh criterion?

A

Two points sources are just resolved if the first minimum of the diffration pattern of one occurs at the same angle as the central maximum of the other.

20
Q

Apply the Rayleigh’s criterion to a picture through a narrow slit

A

The images of two sources can be just resolved through a narrow slit, of width b, if they have an angular separation of:

21
Q

Apply the Rayleigh’s criterion to a picture through a circular aperture

A

The images of two sources can just be resolved through a circular aperture if they have an angular separation of:

22
Q

What is the significance of resolution in radio telescopes?

A
  • Detect wavelengths longer than visible light
  • Require big diameters in order to have big resolution
23
Q

What is the significante of resolution in electron microscopes?

A
  • Electron waves are detected by a fluorescent screen or sensors
  • The size of atoms is much smaller than the wavelength of visible light
  • Idk the book doesn’t even say
24
Q

What is the significance of resolution in digital cameras?

A
  • The sizes of the lens and aperture affect the resolution
  • Distance between the pixels must be small enough to resolve the detail provided by the lens
25
Q

What is the significance of resolution in CDs and DVDs?

A
  • The closer the lands and pits are located to each other, the greater the amounf of information that can be stored
  • If the lands are too close together, the diffracting laser beam cannot resolve the difference between them → a laser with a shorter wavelength needs to be used
26
Q

What is meant by polarised light?

A

Electromagnetic waves are (plane) polarised if all the electric field oscillations are only in one plane

27
Q

What is meant by polarisation by reflection?

A

When unpolarised light reflects off an insulator the waves may become polarised and the plane of polarisation will be parallel to the reflecting surface (water surface etc)

28
Q

What is Brewster’s law?

A

Used to calculate Brewster’s angle:

n = tan*ϕ *

29
Q

What is Brewster’s angle?

A

The angle at which all of the reflected light is polarised = when the refracted rays and the reflected rays are exactly at 90° angle to each other

30
Q

What is a polariser?

A

A special filter that is used to convert unpolarised light into polarised light by absorbing oscillations in all planes except one

31
Q

What is an analyser?

A

A second filter used after a polariser, which can be rotated to analyse light to determine if it is polarised and in which direction

32
Q

What is Malus’ law?

A

I = I0cos2θ

33
Q

What is an optically active substance?

A

A substance which rotates the plane of polarisation of light waves passing through it.

34
Q

How can polarisation be used to determine the concentration of certain solution?

A

The greater the concentration of an optically active substance, the more the plane of polarisation is rotated.

35
Q

How can polarisation be used in stress analysis?

A
  • Some plastics ang glasses become optically active and rotate the plane of polarisation of light when they are stressed
  • The greater the stress, the greater the rotation of the plane of polarisation
  • A transparent material is placed between polarising filters and put under the action of various forces
36
Q

Outline the function of liquid-crystal displays (LCD)

A
  • A liquid crystal is a state of matter that has physical properties between a liquid and a solid
  • The ability to polarise can be changed by applying a small potential difference
  • If there is no p.d., no light is transmitted out of the analyser
  • When a p.d. is applied, its molecules change orientation
  • The plane of polarisation rotates and some or all of the light is transmitted
  • The amount of rotation and the amount of light transmitted depend on the size of the p.d.
  • In displays, light entering through the front passes through the liquid crystals and is then reflected back to the viewer
  • Each segment of the display will appear dark or light, depending whether a p.d. has been applied

Physics (16 decks)

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