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35 Cards in this Set
- Front
- Back
What are the laws of refraction of light?
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1. Snell's law: ratio of sini/sinr is constant.
2. Incident ray, refracted ray and normal are all in the same plane. |
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How is the refractive index calculated?
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1. n = ci / cr
2. n = sini/sinr |
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What is meant by critical angle?
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The angle above which total internal reflection occurs.
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What conditions lead to total internal reflection?
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When light is travelling in a more dense material towards a less dense material has an angle of incidence greater than the critical angle total internal reflection occurs.
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How is refractive index related to the critical angle?
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n = 1 / sinC
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What can total internal reflection be used for?
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Endoscopy, transmitting data.
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What is multipath dispersion?
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Where different rays of light follow different paths down the optical fibre, taking different times.
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What are the effects of multipath dispersion?
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The data becomes distorted/spread out/smeared/blurred.
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How is multipath dispersion overcome?
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By using a monomode fibre (very narrow fibre), so that most of the light goes straight down the middle.
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What is meant by the term displacement?
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How far the particle is from its rest position.
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Define amplitude.
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The maximum displacement of a particle.
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Define period.
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The time between consecutive events. T=1/f
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Define phase difference.
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How many degrees or radians a first wave is out of phase with a second wave.
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Define frequency.
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The number of similar events (eg waves) per unit time (eg second).
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Define wavelength.
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The distance between similar points on adjacent waves. (eg crest to crest)
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What is the equation linking frequency, wavelength and speed?
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v = f lambda
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What do progressive waves transfer?
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Energy. not matter (no nett movement of particles).
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Describe how a transverse wave is formed.
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The particles vibrate in a direction perpendicular to the direction of travel of the wave.
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What is the speed of a wave?
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How fast the wave moves. The distance travelled per second by a crest.
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Describe how a longitudinal wave is formed.
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The particles vibrate backwards and forwards, along the direction of travel of the wave.
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Which type of waves does polarisation affect?
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Transverse waves only.
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What is polarisation?
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In unpolarised light the electric anf magnetic fields vibrate in all directions. In polarised light each vibrates in only one direction.
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What causes polarisation?
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Passing a transverse wave through a polar.
By reflection. By scattering. |
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What changes occur when a wave enters a different medium?
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Its wavelength and velocity cahnge. Its frequency does NOT CHANGE.
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Should I know how to measure frequency using an oscilliscope?
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YES - go and find out!!
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What is the principle of superposition?
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At any moment, the resultant displacement is the sum of the displacements of the individual waves.
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What is constructive interference?
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When the waves are in phase (ie path differnce = nlambda). High intensity, eg louder sounds.
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What is destructive interference?
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When the waves are out of phase (ie path difference = n+1/2lambda.
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What is meant by the term coherence?
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Coherent waves have the same frequency and wavelength. They must have a constant phase difference.
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Define diffraction.
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The spreading out of waves as they pass through a gap similar to their wavelength or barrier edge.
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Should I know how to practically demonstrate diffraction?
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YES - using a ripple tank, with narrow and wide gap.
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SHould I know how to carry out Young's slits experiment?
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YES.
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What conditions are needed for Young's slits experiment?
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Using a laser: double slits 1mm apart; screen 3m away; laser with wavelength about 500nm.
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What does Young's slits demonstrate?
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That interference and diffraction occur with light; proving it is acting as a wave.
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What is the equation for Young's slits experiment?
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lambda = ax/D
a - slit separation x - fringe width D - distance to screen |