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### 35 Cards in this Set

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