CHAPTER 16: WAVES-1 16.2. Interference · CHAPTER 16: WAVES-1 16.2. Interference standing waves and...

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A. La Rosa Lecture Notes PH-213 GENERAL PHYSICS ________________________________________________________________________ CHAPTER 16: WAVES-1 16.2. Interference standing waves and resonance Interference of travelling waves Case 1 Waves travelling in the same direction Case 1A Interference between waves of the same frequency Case 1B Interference between waves of slightly different frequency (This case will be done in Chapter 17) Case 1C Coherent waves Case 2 Waves travelling in opposite direction Standing waves Resonance of waves in a string Case 2A String attached at one end Intuitive solutions, analytical solutions Case 2B String attached at both ends Intuitive solutions, analytical solutions

Transcript of CHAPTER 16: WAVES-1 16.2. Interference · CHAPTER 16: WAVES-1 16.2. Interference standing waves and...

Page 1: CHAPTER 16: WAVES-1 16.2. Interference · CHAPTER 16: WAVES-1 16.2. Interference standing waves and resonance Interference of travelling waves Case 1 Waves travelling in the same

A. La Rosa Lecture Notes

PH-213 GENERAL PHYSICS ________________________________________________________________________

CHAPTER 16: WAVES-1

16.2. Interference standing waves and resonance

Interference of travelling waves

Case 1 Waves travelling in the same direction Case 1A Interference between waves of the same

frequency Case 1B Interference between waves of slightly different

frequency (This case will be done in Chapter 17) Case 1C Coherent waves

Case 2 Waves travelling in opposite direction Standing waves Resonance of waves in a string

Case 2A String attached at one end Intuitive solutions, analytical solutions Case 2B String attached at both ends Intuitive solutions, analytical solutions

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CASE-1 Waves travelling in the same direction
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CASE-1A Interference between two harmonic waves of the same frequency w (therefore, the same k) but different phase
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Df
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Dx
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Df = k Dx
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Interference of travelling waves
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Interference (synonymous of addition of waves)
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Interference factor
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Same phase
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Peaks and valleys coincide
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Example: Full constructive interference case ( f = 0 )
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different phase
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Particular case: Dx =l/2
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Example: Destructive interference case ( f = p )
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Dx
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(2)
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(1)
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P
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Q
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B
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P and Q are in phase
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A and B are out of phase by (k) (2 Dx)
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A
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Example: Controlling the degree of interference ( 0 < f < 2p )
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Before the reflection
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After the reflection
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draw
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Lens
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FIGURE-1
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FIGURE-2
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CASE-1B Interference between waves of slightly different frequency (This case will be done in Chapter 17)
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CASE-1C Coherent waves
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CASE-2 Waves travelling in the opposite directions
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Standing Waves
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and this is what happens:
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f1
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Fig. Solutions obtained by intuition
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Resonance of waves in a string
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Case 2A String fixed at one end
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Intuitive solutions
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For the case when one end of the string is fixed
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...
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Analytical solution
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General solution.
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But we have to impose the particular boundary conditions of the problem (i.e. that the string is fixed at one end)
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satisfy
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L
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Case 2B String fixed at both ends
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Intuitive solutions
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Analytical solution
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This is a generalization of the example (to be worked out in the next page) for the case of having jut two particles
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