Today 1/17

1
Today 1/17

• Interference
• HW 1/17 HW Handout Interference Due Thur,
  1/23 (beginning of class)
• Todays goalPredict locations where
  constructive and destructive interference occur.

2
This picture now includes the sources of the
waves.
In this case the sources are in sync and
produce waves of equal wavelength. The wave
velocity depends only on the medium and so is the
same for both.
Source 1
Source 2
3
This picture now includes the sources of the
waves.
In this case the sources are in sync and
produce waves of equal wavelength. The wave
velocity depends only on the medium and so is the
same for both.
Source 1
Source 2
4
This picture now includes the sources of the
waves.
In this case the sources are in sync and
produce waves of equal wavelength. The wave
velocity depends only on the medium and so is the
same for both.
Source 1
Source 2
5
This picture now includes the sources of the
waves.
In this case the sources are in sync and
produce waves of equal wavelength. The wave
velocity depends only on the medium and so is the
same for both.
Source 1
Source 2
6
This picture now includes the sources of the
waves.
In this case the sources are in sync and
produce waves of equal wavelength. The wave
velocity depends only on the medium and so is the
same for both.
Source 1
Source 2
7
This picture now includes the sources of the
waves.
In this case the sources are in sync and
produce waves of equal wavelength. The wave
velocity depends only on the medium and so is the
same for both.
Source 1
Source 2
8
This picture now includes the sources of the
waves.
In this case the sources are in sync and
produce waves of equal wavelength. The wave
velocity depends only on the medium and so is the
same for both.
Source 1
Source 2
9
This picture now includes the sources of the
waves.
In this case the sources are in sync and
produce waves of equal wavelength. The wave
velocity depends only on the medium and so is the
same for both.
Source 1
Source 2
10
This picture now includes the sources of the
waves.
In this case the sources are in sync and
produce waves of equal wavelength. The wave
velocity depends only on the medium and so is the
same for both.
Source 1
Source 2
11
This picture now includes the sources of the
waves.
In this case the sources are in sync and
produce waves of equal wavelength. The wave
velocity depends only on the medium and so is the
same for both.
Source 1
Source 2
12
This picture now includes the sources of the
waves.
In this case the sources are in sync and
produce waves of equal wavelength. The wave
velocity depends only on the medium and so is the
same for both.
Source 1
Source 2
13
This picture now includes the sources of the
waves.
In this case the sources are in sync and
produce waves of equal wavelength. The wave
velocity depends only on the medium and so is the
same for both.
Source 1
Source 2
14
This picture now includes the sources of the
waves.
In this case the sources are in sync and
produce waves of equal wavelength. The wave
velocity depends only on the medium and so is the
same for both.
Source 1
Source 2
15
This picture now includes the sources of the
waves.
In this case the sources are in sync and
produce waves of equal wavelength. The wave
velocity depends only on the medium and so is the
same for both.
Source 1
Source 2
16
This picture now includes the sources of the
waves.
In this case the sources are in sync and
produce waves of equal wavelength. The wave
velocity depends only on the medium and so is the
same for both.
Source 1
Source 2
How would your answer change if the sources were
out of sync?
Where are the locations of constructive and
destructive interference?
17
This picture now includes the sources of the
waves.
Out of sync means that one produces a crest while
the other produces a trough--its a timing thing.
Source 1
Source 2
How would your answer change if the sources were
out of sync?
18
This picture now includes the sources of the
waves.
Out of sync means that one produces a crest while
the other produces a trough--its a timing thing.
Source 1
Source 2
How would your answer change if the sources were
out of sync?
19
This picture now includes the sources of the
waves.
Out of sync means that one produces a crest while
the other produces a trough--its a timing thing.
Source 1
Source 2
How would your answer change if the sources were
out of sync?
20
This picture now includes the sources of the
waves.
Out of sync means that one produces a crest while
the other produces a trough--its a timing thing.
Source 1
Source 2
How would your answer change if the sources were
out of sync?
21
This picture now includes the sources of the
waves.
Out of sync means that one produces a crest while
the other produces a trough--its a timing thing.
Source 1
Source 2
How would your answer change if the sources were
out of sync?
22
This picture now includes the sources of the
waves.
Out of sync means that one produces a crest while
the other produces a trough--its a timing thing.
Source 1
Source 2
How would your answer change if the sources were
out of sync?
23
This picture now includes the sources of the
waves.
Out of sync means that one produces a crest while
the other produces a trough--its a timing thing.
Source 1
Source 2
How would your answer change if the sources were
out of sync?
24
This picture now includes the sources of the
waves.
Out of sync means that one produces a crest while
the other produces a trough--its a timing thing.
Source 1
Source 2
How would your answer change if the sources were
out of sync?
25
This picture now includes the sources of the
waves.
Out of sync means that one produces a crest while
the other produces a trough--its a timing thing.
Source 1
Source 2
How would your answer change if the sources were
out of sync?
26
This picture now includes the sources of the
waves.
Out of sync means that one produces a crest while
the other produces a trough--its a timing thing.
Source 1
Source 2
How would your answer change if the sources were
out of sync?
27
This picture now includes the sources of the
waves.
Out of sync means that one produces a crest while
the other produces a trough--its a timing thing.
Source 1
Source 2
How would your answer change if the sources were
out of sync?
28
This picture now includes the sources of the
waves.
Out of sync means that one produces a crest while
the other produces a trough--its a timing thing.
Source 1
Source 2
How would your answer change if the sources were
out of sync?
29
This picture now includes the sources of the
waves.
Out of sync means that one produces a crest while
the other produces a trough--its a timing thing.
Source 1
Source 2
How would your answer change if the sources were
out of sync?
30
This picture now includes the sources of the
waves.
Out of sync means that one produces a crest while
the other produces a trough--its a timing thing.
Source 1
Source 2
How would your answer change if the sources were
out of sync?
31
This picture now includes the sources of the
waves.
Out of sync means that one produces a crest while
the other produces a trough--its a timing thing.
Source 1
Source 2
How would your answer change if the sources were
out of sync?
32
This picture now includes the sources of the
waves.
Out of sync means that one produces a crest while
the other produces a trough--its a timing thing.
Source 1
Source 2
How would your answer change if the sources were
out of sync?
33
This picture now includes the sources of the
waves.
Out of sync means that one produces a crest while
the other produces a trough--its a timing thing.
Source 1
Source 2
How would your answer change if the sources were
out of sync?
34
This picture now includes the sources of the
waves.
Out of sync means that one produces a crest while
the other produces a trough--its a timing thing.
Sources out of phase (out of sync)
Source 1
Source 2
How would your answer change if the sources were
out of sync?
Now the locations for constructive and
destructive interference switch!
35
In any case, the interference occurs in a
pattern. The next job is to invent a rule so we
can predict these locations.
Sources out of phase (out of sync)
Source 1
Source 2
36
What do you need to predict interference?
1. Whether the sources are in phase or not
2. Wavelength
3. Location
Sources out of phase (out of sync)
Source 1
Source 2
37
PL1
PL2
The difference in distance from each source to
constructive locations is given by...
We want one thing we can say about all these
places for in phase and constructive.
PL2 - PL1 Path Length Difference PLD n?, n
0,1,2,3...
Sources out of phase (out of sync)
Source 1
Source 2
38
The difference in distance from each source to
destructive locations is given by...
Now what can we can say about the places for in
phase and destructive.
Path Length Difference PLD (n 1/2)?, n
0,1,2,3...
Sources out of phase (out of sync)
Source 1
Source 2
39
The difference in distance from each source to
constructive locations is...
Path Length Difference PLD (n 1/2) ?, n
0,1,2,3...
What about the places for out of phase and
constructive.
Sources out of phase (out of sync)
Source 1
Source 2
40
The difference in distance from each source to
destructive locations is...
Path Length Difference PLD n?, n 0,1,2,3...
What about the places for out of phase and
destructive.
Sources out of phase (out of sync)
Source 1
Source 2
41
Summary
In phase, constructive
PLD n?, n 0,1,2,3...
PLD (n 1/2)?, n 0,1,2,3...
In phase, destructive
Out of phase, constructive
PLD (n 1/2)?, n 0,1,2,3...
Out of phase, destructive
PLD n?, n 0,1,2,3...
Sources out of phase (out of sync)
Source 1
Source 2
42
Interference in 2-DSources in phase
Crest
Trough
43
Interference in 2-DSources in phase
Crest
Trough
44
Interference in 2DSources out of phase
Crest
Trough
45
Interference in 2-DSources out of phase
Crest
Trough