Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
35 Cards in this Set
- Front
- Back
|
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 |
