Waves Flashcards
What is Superposition
Superposition: When two waves meet at any point, the displacement at that point is the net displacement of caused by each wave.
What are Coherent waves
Waves which have the same frequency and a constant phase relationship
Constructive Interference
When two waves in phase, interfere and produce maximum amplitude.
Known as Maxima too
Destructive interference
When two waves meet in anti phase/ when path difference is (n+0.5) λ minimum amplitude is produced.
Why is Coherence important
Ensures that at a certain point, a certain amplitude is produced therefore a stable interference pattern is produced
Path Dfference
The difference in the distance travelled by two waves from their respective sources to a given point
When does a wave crest meets a wave crest.
When distance travelled by both waves are whole numbers of wavelengths, constructive interference takes place and the crest meets the crest
In Phase meaning ( 2 marks)
When two waves have a path difference of even number of 1/2 λ and a phase difference of 2 π , 4 π , 6 π
Anti-Phase ( 2 marks)
When the path difference between two waves is ( n +1/2 λ) and when the phase difference is 180° or π, 3 π, 5 π
Explain the interference pattern ( 4 marks)
- Two waves having the same frequency, amplitude and constant phase relationship.
- Meet and superpose.
- When they meet in phase and path difference is even number of 1/2 λ, constructive interference takes place and maximum amplitude is produced
- When they meet in anti phase and path difference is odd number of half λ, destructive interference takes place. Minimum amplitude per is produced.
How to observe Interference in Ripple tank
Connect two dippers to the same motor. Dippers should be JUST TOUCHING the water in a leveled tank.
Circular wavefronts will by generated.
Use a stereoscope to freeze the pattern shown by the water waves
Stereoscope has to be equal to the frequency of the waves
In the interference pattern, why does the zero order maxima have the greatest amplitude
They have a path difference of 0.
Distance travelled by each wave is equal
Why is a narrow slit initially needed for the Young’s Double slit experiment and which type of light does not require it
To allow a small portion of monochromatic light to pass through the slit.
Laser does not need it
Young’s Double Slit Experiment
The two slits are the points where waves diffract. They act as coherent sources of waves. The diffracted have constant phase relationship and same frequency. The Waves meet and Superpose. When in phase, maximum amplitude is produced and a bright fringe is observed on the screen
When in anti phase, minimum amplitude is produced and a darker fringe is observed.
The maximum brightness is observed on mid fringe.
Fringe separation is measured from mid fringe to mid fringe
Young’s double slit experiment equation
a Δx
λ= ———
D
Where a is slit separation
Δx is the fringe separation
D is the distance between the slit and the screen
