5: Waves and Particle Nature of Light Flashcards

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1
Q

Describe longitudinal waves in terms of pressure variation.

A
  • Wave consists of alternate compressions and rarefactions
  • Compressions have increased pressure
  • Rarefactions have decreased pressure
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2
Q

Describe longitudinal waves in terms of the displacement of molecules.

A
  • Wave consists of alternate compressions and rarefactions
  • Particles are displaced towards the points of compression and away from the points of rarefaction
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3
Q

Describe transverse waves.

A

Vibration is at right angles to the direction of travel.

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4
Q

Explain how a standing wave is set up on a string.

A
  • 2 waves travelling in opposite directions superpose.
  • Constructive when waves are in phase, destructive when waves are in antiphase.
  • Antinodes (max amplitude) are formed from points of constructive interference, nodes (min amplitude) are formed from points of destructive interference.
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5
Q

What is meant by a real image?

A

Light rays pass through the actual image.
Rays converge to a point and can be projected on a screen.

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6
Q

What is a wavefront?

A

A line on a wave along which all points are in phase.

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7
Q

State what is meant by diffraction.

A

Spreading out of a wave as it passes through an apature.

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8
Q

State the principle of superposition of waves.

A

When two or more waves meet, the total displacement at a point is the sum of the individual displacements.

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9
Q

State what is meant by refraction.

A

Change in direction of a wave, due to a change in optical density.

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10
Q

State what is meant by critical angle.

A

The angle of incidence in an optically denser medium that has an angle of refraction of 90 degrees.

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11
Q

State what is meant by plane polarised light.

A

Oscillations in one plane only.
Plane includes direction of propagation.
or
Oscillations in one direction, perpendicular to direction of propagation.

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12
Q

Explain how the photoelectric effect supports the particle model of light. (6)

A
  • Electrons emitted instantly
  • No emission below the threshold frequency
  • Max ke is independent of the intensity
  • Rate of emission is proportional to the intensity
  • One photon is absorbed by one electron
  • With waves, energy can build up
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13
Q

Explain the process that results in an emission spectrum. (7)

A
  • Electrons absorb energy,
  • Electrons move to higher energy levels,
  • A photon is released when an electron drops down energy levels,
  • Electrons have discrete energy levels,
  • Energy of the photon = difference between energy levels,
  • E = hf, so frequency is determined by difference in energy levels,
  • Only certain energy changes possible, so only certain frequencies are emitted.
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