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Physics > Waves > Flashcards

Waves Flashcards

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1
Q

Define wavefront

A

The surface made up of all the points of the wave that are in phase with each other.

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2
Q

Define displacement

A

How far a wave has travelled from its undisturbed position.

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3
Q

Define phase

A

The measurement of a certain points position along the wave cycle.

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4
Q

Define longitudinal

A

Oscillations occur parallel to the direction of travel

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5
Q

How does a standing wave form?

A

Two waves are travelling in opposite directions and superimpose continuously to form a standing wave.

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6
Q

What are the conditions for waves to be able to form a standing wave

A

They need to be coherent (same frequency and a constant phase relationship)

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7
Q

Do standing waves transfer energy?

A

No they don’t

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8
Q

Where does the node occur when a standing wave is formed between two points

A

At each end

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9
Q

Define diffraction

A

The spreading out of waves as they pass through an obstruction

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10
Q

How does Huygens explain diffraction

A

Huygens suggested that every point on a wavefront can be considered to be a point source of secondary waves (which he called wavelets)

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11
Q

Define wave front

A

A line that marks point all in phase

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12
Q

How does the electron gun experiment work?

A

Electrons are accelerated in an electron gun to a high potential and are then directed through a thin film of graphite. The lattice structure of the graphite acts like the slits in a diffraction grating.
The electrons diffract from the gaps between carbon atoms and produce a circular pattern on a fluorescent screen made from phosphor.

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13
Q

Define the critical angle

A

The angle at which the angle of refraction is 90 degrees

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14
Q

What are the properties of an image formed by a converging lens

A
  • Real
  • Inverted
  • Magnifies
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15
Q

What are the properties on a diverging lens image?

A
  • Upright
  • Diminished
  • Virtual
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16
Q

What is polarisation?

A

The filtering of an electromagnetic wave so that it only oscillated in one plane (direction)

17
Q

Can sound be polarised?

A

No only transverse light can be polarised

18
Q

What is the evidence for the wave properties of light?

A
  • Interference
  • Polarisation
  • Diffraction
19
Q

What is the evidence of particle properties of light?

A
  • Travels in a straight line (shadows)
  • Photoelectric effect
20
Q

Define work function

A

The minimum energy of incident photons to release electrons from the surface

21
Q

What is the photoelectric effect

A

When light is incident on a surface, electrons absorb photons so they have enough energy to be released from the surface

22
Q

Define thermionic emission

A

A metal will release electrons when it is heated

23
Q

True or false:
Two points λ/2 apart oscillate with the same amplitude

A

True

24
Q

What effect does the speed of electrons have on the diameter of rings in the electron gun experiment.

A

Inversely proportional.
(Decreasing speed increases diameter)

25
Q

State 2 ways to improve accuracy when measuring the refractive index of glass.

A
  • Use a large angle of incidence
  • Use a narrow ray
  • Work in a dark room
  • Repeat and calculate a mean
26
Q

Why do atoms only emit a certain frequency of radiation?

A
  • Electrons exist in discrete energy levels
  • Energy is proportional to frequency so frequency is also discrete
  • Eventually all atoms will return to a lower state/ ground state as this is the most stable
  • Atoms won’t absorb electrons/energy outside the discrete numbers
  • As the atoms deexcites a photon is emitted
27
Q

Why is there a bright spot equidistant from two slits?

A
  • The distance is the same so path difference is zero
  • So the waves will arrive in phase
  • So constructive interference occurs
28
Q

For the equation m = v / u
explain what v and u represent.

A

V is the distance of the image to the lens
U is the distance of the object to the lens

29
Q

Explain a method to find the focal length of a converging lens

A
  • Focus an image of a far object onto a screen
  • Measure distance of lens to the screen
30
Q

Why is a lens with a shorter focal length thicker at its centre?

A
  • Light gets refracted by a greater amount
  • So rays converge at a point closer to the lens
31
Q

What does the thin metal foil experiment show?

A

The diffraction experiment indicates electrons have wave nature.
Therefore electrons behaviour has wave-particle duality.

32
Q

What is an infinite source?

A

Light from the source is parralel

33
Q

What is a real image

A

An image that can be projected onto a screen

Physics (9 decks)

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