What is an antinode
Maximum amplitude (in phase)
What is a node
Minimum amplitude (anti-phase)
What is the fundamental mode
1st harmonic
How is a stationary wave formed in a flute
Incident and reflected waves are superimposed at specific frequencies
What are closed ends
Nodes (Min amplitude)
What are open ends
Antinodes (Max amplitude)
What is a pressure node
Displacement antinode
What is a pressure antinode
Displacement node
Difference between constructive and destructive interference
Path difference
C: n(wavelength)
D: (n+0.5)(wavelength)
Phase difference
C: Even no. pi
D: Odd no. pi
Explain how a bright fringe is observed
- Path difference of the 2 waves is n(wavelength)
- 2 waves leave the 2 slits in phase and arrive in phase
- Constructive interference occurs
- Bright fringe observed
Explain how a dark fringe is observed
- Path difference of the 2 waves is (n+0.5)(wavelength)
- 2 waves leave the 2 slits in phase and arrive in anti-phase
- Destructive interference occurs
- Dark fringe observed
Formula for double slit interference
x=D(wavelength)/a
What are the assumptions for double slit interference
- wavelength «_space;a «_space;D
- Small angle approximation holds
- Light rays are approximately parallel
Default number of diffraction grating lines per metre
5x10^5
Condition for 2 diffraction patterns to be distinguishable
Central maximum of one diffraction patterns must lie on first minimum of the other diffraction pattern
Explain why stationary waves on strings only occur at specific frequencies
- Stationary wave is formed only when ends of string are nodes (anti-phase, min amplitude)
- Only specific wavelengths and hence specific frequencies matching natural frequency of string can form stationary waves
Why is it impossible to observe interference fringes between light beams plane polarised
- Resultant intensity is always constant
- No destructive regions
- No interference pattern observed
Explain changes when intensity of one light on one slit is reduced in double slit
- Intensity of bright fringe decreases
- Intensity of dark fringe increases
Explain changes when slit width is reduced in double slit
- No change in slit separation
- Intensity of bright fringe decreases
- Intensity of dark fringe remains same
- No. of fringes increases
Explain why when white light incident on single slit, central fringe is coloured at edges and has white central region
- White light consists of various wavelengths of light
- Different wavelengths of light have different angles of diffraction
- At centre all wavelengths undergo constructive interference to form central white region
Why do intensities of double slit fringes decrease further from central maxima
- Waves exiting double do not behave as point sources
