5. Wave properties Flashcards
What is the principle of superposition?
When 2/more waves (of the same type) occupy the same position in space then the resultant wave is found by the vector sum of the individual displacements of the waves at any point
When two or more waves cross at a point, the displacement at that point is equal to the sum of the displacements of the individual waves
Gl o7
Define constructive interference?
- Same type of wave (transverse)
- Waves are in-phase
- Waves reinforce each other to produce a larger wave
Define destructive interference?
- Same type of wave (transverse)
- Waves are anti-phase
- Waves cancel each other to produce a smaller wave
Define total destructive interference?
Produces a zero resultant wave known as cancellation
Should be easy to know how to draw resultant wave forms with principle of superposition
I believe
How is a stationary wave formed?
Interference of:
- Two progressive waves
- Of same frequency & amplitude
- Travelling in opposite directions
Alternate name for stationary waves?
Standing waves
How are stationary waves commonly set up?
- Wave reflecting back from a surface
- Reflected waves interfere with original wave
Explain stationary waves?
- Incident wave & reflected wave
- Interfere each other
- Superposition happens
- Only certain frequencies to result resonance condition
Explain nodes
Places along wave w/ zero displacement
Destructive interference
Explain antinodes
Places between nodes that oscillate & suffer maximum displacement
- range of (maximum) constructive and destructive interference occur here
Formula for distance between adjacent nodes/adjacent antinodes?
Inter-nodal spacing is λ/2
State the amplitude for a stationary wave?
Varies between 0 and 2A
State the amplitude for a progressive wave?
A for all particles as the wave travels
State the frequency for a stationary wave?
Same for all particles except at nodes
State the frequency for a progressive wave?
Same for all particles
State the energy for a stationary wave?
No transfer
(energy stored within each loop)
State the energy for a progressive wave?
Energy transfer
State the waveform for a stationary wave?
Does not advance
State the waveform for a progressive wave?
Advances at the speed of wave
State the phase for a stationary wave?
All particles vibrate in-phase within a loop
(adjacent loops in antiphase)
State the phase for a progressive wave?
- Over one wavelength
- Particles have a range of phases between 0 and 2π
Explain standing waves in a string?
String can be vibrated to form a stationary wave with both ends fixed
Both ends form nodes
Explain standing waves in a closed pipe?
Vibrating column of air with one end closed and the other open
One one forms a none the other an antinode
Explain standing waves in an open pipe?
Vibrating column of air with bond ends open
Both ends form antinodes
State the formula of wavelength for their first harmonic within string and open pipe standing waves
λ = 2l
State the formula of wavelength for their first harmonic within closed pipe standing waves
λ = 4l
Formula for when u increase harmonic of string and open pipe standing waves?
2nd - λ2 = l
3rd - λ3 = 2l/3
4th - λ4 = l/2
5th - λ5 = 2l/5
I could or may seem to understand the pattern
Formula for when u increase harmonic of closed pipe standing waves?
2nd - impossible
3rd - λ3 = 4l/3
4th - impossible
5th - λ5 = 4l/5
The trick is every odd n°
In addition, this the only different between the other 2
State 5 stationary wave experiments
- Stationary waves on a string/wire
- Stationary mechanical waves on a wire loop
- Stationary Em waves using microwaves
- Stationary sound waves in closed pipes
- Measuring the speed of sound using a closed tube
U may add cards related to the 5 other experiments somehow
Hm
What is diffraction of a wave?
The spreading out of a wave’s energy around obstacles and through gaps
For a diffraction thru gap, what happens when gap width decreases?
If gap width decreases, amount of diffraction (angle of spread) increases
When does maximum diffraction occur?
Gap width equal/slightly smaller than λ
When is the diffraction effect at its greatest?
Wavelength is equal to/slightly greater than the obstacle or the gap width
Explain coherent sources during 2 source interference
- Coherent when they produces waves of same freq
- Same amplitude and maintain constant phase difference
2 examples of coherent wave source?
- Laser
- Single slit aperture
Explain incoherent wave sources during 2 source interference
- 2 sources of waves having different frequencies
-Will have phases constantly changing - Therefore pattern produces constantly changing
2 examples of incoherent wave sources?
- Sunlight
- Light bulbs
Formula for interference fringe separation formula?
(in data booklet)
λ = (a△y)/D
Explain each symbol within interference fringe separation formula
(all must be in m units)
λ = (a△y)/D
λ - wavelength (m)
a - source separation (m)
D - distance from source (m)
△y - fringe separation (m)
What is path difference?
- The difference in distance that two waves must travel
- From their sources to a given point
Explain how an interference pattern is formed?
If the light from two point sources overlaps, the interference pattern maps out the way in which the phase difference between the two waves varies in space
Probably can’t learn in time
How is a double slit experiment set up?
Need:
- Monochromatic light source
- Single slit
allowed for single wave from to reach double slits
- Double slits
All wave fronts gon’ be in phase,
Thus shall emit coherent waves
What is meant by monochromatic light?
single-wavelength light
In a double slit experiment, explain the bright fringes seen
- Constructive intereference
- Between 2 beams coming from both slits
- Must be arriving in-phase
In a double slit experiment, explain the dark fringes seen
- Destructive interference
- Between 2 beams coming from both slits
- Must be arriving out-of-phase
How to make double slit method more accurate?
Add more slits….
What is diffraction grating?
Consisting of many narrow, parallel and equally spaced slits that transmit light
3 advantages of using diffraction grating?
- More light can pass thru = fringes r brighter
- Fringes more well-defined, better cancellation either side of centre of fringe
- Fringes more spread out due to much smaller slit separation
What is the formula for diffraction grating?
(it’s in data booklet, tho reversed)
nλ = dsinθ
Explain each symbol within formula of diffraction grating
(units gotta be m mostly)
nλ = dsinθ
n - order number
λ - wavelength (m)
d - slit separation (m)
θ - angular position of order from centre (degrees)
How do u derive for nλ = dsinθ?
First, look between 2 slits and make some right angled triangle?
Honestly, better if u had a picture, too bad u can’t place any
1. AC is the path difference between the adjacent waves
2. For 2 adjacent waves the path difference AC = dsinθ
3. At a bright maxima the waves are in-phase
4. Therefore, AC = nθ
5. Equating gives: nλ = dsinθ
Describe the appearance of the diffraction pattern from white light incident upon a diffraction grating
The central maxima is narrow and white. The surrounding maxima are split into the colours red - violet. The fringes get broader with each other. Eventually the colours overlap.
Hope for the best
