Waves and optics Flashcards
Define longitudinal waves
In longitudinal waves, the vibrations are parallel to the direction of wave travel
Define transverse waves
In transverse waves, the vibrations are at right angles to the direction of wave travel.
Define amplitude
A waves maximum displacement from it’s equilibrium position
Define frequency
The number of waves that pass a point in a unit time
f= 1/T
Define period
Time takes for a wave to complete a cycle
T= 1/f
Define wavelength
The distance between two identical positions on two adjacent waves (eg. peak to peak)
What type of waves polarise?
Only transverse waves
The EM spectrum:
Which has the highest wavelength?
Which has the highest frequency?
Radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, gamma rays
Highest wavelength: Radio
Highest frequency: Gamma
What conditions are necessary to produce a stationary wave?
Two waves travelling in opposite directions along the same line of travel and in the same plane.
The waves have the same speed.
The waves have the same frequency.
The waves have the same approximate amplitude.
Define interference
(vs superposition?)
When two waves meet while travelling along the same medium and interact. It is observed.
Superposition is the sum of the displacements. It is the effect.
What makes two waves coherent?
In phase
Constant phase difference
Similar amplitudes
For constructive interference to occur, what must the phase difference be?
nλ
For destructive interference to occur, what must the phase difference be?
(n+1/2)λ
In double slit diffraction, what effect does increasing the distance between the slits and the screen cause?
Increasing fringe width
w = λD/s
In double slit diffraction, what effect does increasing the slit seperation cause?
Decreasing fringe width
w = λD/s
What does white light look light when diffracted through a single slit?
Bright white central maxima, then black fringes alternating with rainbow fringes either side. For the rainbow fringes, red light is furthest from maxima, and the blue light is closest to maxima.
For a diffraction grating, what is the key equation?
dsinx =nλ
What is refraction?
When light slows down/speeds up and then changes direction
What is Snells law?
n1sinx1 = n2sinx2
When travelling into a more optically dense material, what happens to the light?
It will bend towards the normal
When travelling into a less optically dense material, what happens to the light?
It will bend away from the normal
When does total internal reflection occur?
When the angle of refraction is greater than 90°, the angle of incidence is greater than the critical angle and n1>n2
How can you work out the refractive index of a substance?
n = c / cs
Where c is the speed of light in a vacuum and cs is the speed of light in the substance
How can you work out the critical angle?
sin xc = n2/n1
Angular frequency equation?
w=2 pi f
