9. Wave phenomena Flashcards
Define amplitude in SHM
The maximum magnitude of displacement from the equilibrium position
Define angular frequency (omega)
Rate of angular displacement
Define SHM
An oscillatory motion of a particle whose acceleration is directly proportional to its displacement from the equilibrium position and this acceleration is always directed towards that position
Define phase difference
The difference in phase angle between the 2 oscillations which have the same frequency/velocity
When is KE of a particle in SHM maximum?
At equilibrium position
When is PE of a particle in SHM maximum?
At the amplitudes
Visualise the graph of total energy against displacement
KE - sin
PE - cos
Visualise the graph of energy against time
Depends on where x starts at when t=0
If a particle in SHM moves to the right, where is the acceleration towards?
The left. Vice versa.
In circular motion, where does v point towards?
Tangent of the circle
In circular motion, where does ‘a’ point towards?
Center of the circle
What is the intensity profile of diffraction by a single slit like?
Highest peak in the middle, decreases on both sides after the central maxima.
What happens when we increase the slit width?
Intensity increases since more light gets through, but central maxima becomes narrower
What does the area under the graph for the intensity profile represent?
What happens to the area under the graph as the slit width increases?
It represents total energy.
The area under the graph also increases since more light now passes through the slit
What is the modulation effect?
The intensities of the maxima of the double slit pattern is enveloped and bounded by the intensity distribution of the single slit pattern
What is diffraction grating?
An optical component that consists of a large number of parallel equally spaced narrow slits
What happens as the number of slits increase?
The bright peaks grow narrower and more intense
Why is the maxima narrower when there are more slits?
More rays coming in at different angles does not allow for partial constructive interference outside of the optimal angle that gives the maxima. (must be exact)
What is optical path length?
The product of the geometric length of the path followed by light though a given system, and the index of refraction of the medium through which it propagates
L0 = nL
What are the 4 different variations for the 3 mediums for thin film interference?
- Less –> More –> Less
- More –> Less –> More
- Less –> More –> Even more
- Even more –> More –> Less
For the 2 variations with
1. 180 deg phase change
2. No phase change,
what are the equations for constructive & destructive interference?
Constructive: 2dn = (m + 1/2)lamda
Destructive: 2dn = m*lambda
What factors affect the interference of the rays during thin film interference?
Wavelength
Film thickness
Refractive indices
What happens during thin film interference?
When light encounters an interface & a portion of it gets reflected, and the rest pass into the incident medium and get refracted
Basically a combination of the reflected and refracted rays
When do you get multicoloured fringes in thin film interference?
When white light falls onto a thin film & the different wavelengths form fringes at different angles
Definition of resolution
Minimum distance between distinguishable objects in an image
Or: Minimum resolvable distance
What is the Rayleigh criterion?
Two sources are just resolvable when the first minimum of the diffraction pattern of one of the sources falls on the central maximum of the diffraction pattern of the other source
What is the difference in the equation for Rayleigh’s criterion for a circular aperture and a single-slit aperture?
For circular aperture:
theta = 1.22lambda/b
Single-slit aperture:
theta = lambda/b
When is the diffraction pattern unresolved?
When alpha < theta
What is an adaptation of radio telescopes for higher resolution?
Increase b (diameter), so that theta decreases
What is an adaptation of CDs/DVDs for higher resolution?
Reduce the wavelength of light so that theta is decreased
What does resolvance mean?
The ratio of the wavelength of the light to the smallest difference in wavelength that can be resolved by the grating
Or: The ability of a diffraction grating to resolve these wavelengths
Definition of Doppler Effect
The change in measured frequency of a waves that results from the relative motion of a source and/or an observer relative to the medium in which the wave is propagated.
What can you observe about a wave when a source is moving towards an observer?
Higher frequency, shorter wavelength
What can you observe about a wave when an observer is moving with respect to a stationary source?
Higher wave speed, higher frequency
What is the effect of wind blowing from the direction of a stationary source towards a stationary observer?
Higher wave speed, higher wavelength
