Superposition Flashcards
Principle of superposition
When two or more waves meet at a point, the resultant displacement at that point is equal to the vector sum of displacement of the individual waves at that point
What is Interference
When two or more waves superpose according to the principle of superposition
Waves are coherent when..
They have constant phase difference and same frequency
Criteria for steady and observable interference pattern (3)
- Overlapping waves must be coherent (constant phase difference and same frequency)
- Waves have equal amplitude - to achieve complete cancellation
- Must be polarised on the same plane/ unpolarised
Condition for two source interference
The separation between the two slits must be small in comparison to the distance between slits and screen
D»>a
Uses of various apparatus in double slit experiment
Monochromatic light source - gives one frequency/wavelength ( cuz only 1 color )
Single slit - act as point source (achieve coherence)
Double slit - act like two coherent sources of light
Screen - observe interference pattern
When is diffraction most significant?
When size of aperture is same order of magnitude as wavelength of light
Definition of Stationary waves
Result of interference between 2 identical waves of same frequency, amplitude and speed travelling across the same line in opposite directions & overlap
What is Rayleigh’s criterion
When the central maximum of one image falls on the first minimum of another image, the image is distinguishable and said to be just resolved.
Limiting criterion of resolution is known as Rayleigh’s criterion
What is diffraction?
Spreading of waves after they pass through an opening or around an obstacle
What is a stationary wave?
Result of interference between
- two identical waves of same amplitude, frequency and speed
- travelling along the same line in opposite direction
Why is sound heard but source not seen when door is slightly open to a room
For diffraction to be significant, size of aperture should be same order of magnitude as wavelength of wave.
Given wavelength of sound is comparable to that of door gap whereas wavelength of light is much smaller than door gap, there would be more significant diffraction of sound than light
What are the conditions necessary for formation of stationary waves in a pipe
For stationary wave to be formed, the lowest frequency would be obtained when length of pipe correspond to 1/2 of wavelength.
Thus for given frequency of sound, the length of pipe must be adjusted to meet the above relation
State the conditions for a well defined stationary wave using two separate sources (4)
- Two waves have same polarisation axis
- Two waves have same amplitude
- Two waves are travelling in opposite directions and overlap
- Two waves have same frequency and speed
State differences between progressive waves and stationary waves that relate to amplitude, phase and energy.
Amplitude
Stationary: It varies from zero at nodes to maximum at antinodes
Progressive: It is the same for all particles in the wave
Phase
Stationary: Particles within two adjacent nodes are in phase. Particles in alternate segments are in antiphase
Progressive: Wave particles have different ohases within a wavelength
Energy
Stationary: Energy is retained in the vibratory motion of wave
Progressive: There is transfer of energy along the direction of wave propagation
The coloured lights incident on a diffraction grating are now replaced by a single white light source. Suggest the appearance on the bright fringes on the screen.
Central bright fringe is white
The rest of the bright fringes contain a spectrum of colors
