1. Superposition
Superposition is the ability of waves to superimpose (add displacements & energy) as they move through each other.
Constructive interference.
Approaching
Overlapping
Receding

2. Destructive interference .
Approaching
Overlapping
Receding

3. Combining waves of the same f
What happens when two waves are present at the same place at the same time?

4. The Principle of Interference / Superpositioning
For waves:
The resulting wave = the sum of the individual waves
Constructively
Destructive
This applies to all waves: water, light, sound, etc.

5. Interference: What happens when two waves pass through the same region?
When two crests overlap it is called constructive interference. The resultant displacement is larger then the individual ones.
When a crest and a trough interfere, it is called destructive interference. The resultant displacement is smaller.

6. Superposition of Waves
What is the resultant wave pattern
formed when these two waves
overlap?
A. B.
C. D. E. None of these

7. Superposition of Waves
What is the resultant wave pattern
formed when these two waves
overlap?
A. B.
C. D. E. None of these

11. Phase
Two quantities are in phase if they are simultaneously increasing or decreasing, eg V & I are in phase in an AC circuit
Waves in phase

12. Crest of one wave coincide with the trough of the other wave.
2 waves out of phase by ½ a cycle or 180o.
Crest of one wave coincide with the trough of the other wave.

13. Waves out of phase by 90o or a ¼ cycle
If there is a period of time where one quantity is increasing while the other is decreasing they are out of phase.
The two quantities need to have the same frequency (f) but not necessarily the same amplitude to stay in phase.
Waves out of phase by 90o or a ¼ cycle

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15. Beats is a regular pulsing of the loudness of a sound which is heard when two sources produce sounds of slightly different frequency.
fbeat = f1 – f2
For example, when a 552 Hz and a 556 Hz tone are played simultaneously, we hear , or 4 beats per second. The beat frequency is 4 Hz.
Uses ~ Piano Tuning

18. Beats
Let’s say that the tuning fork without a small mass attached has a frequency of 200Hz. If you hear a beat with a frequency of 4 cycles every second, what is the frequency of the tuning fork with the mass on it?
800 Hz
204 Hz
196 Hz
50 Hz

19. Beats
As two notes get closer to being “in tune” with each other (having the same note), what happens to the frequency at which the beats occur?
Increases
Decreases
Stays the same