1. Conceptual Physics
WAVES

2. Review
Transverse waves – particles move _________ to the direction of energy transfer.
Longitudinal waves – particles move ________ to the direction of energy transfer.
Electromagnetic (light) waves – Do/Don’t need a medium through which to travel.
Mechanical waves – Do/Don’t need a medium through which to travel.

3. Check for Understanding
A point is marked on a string. The string is then vibrated so that a transverse wave travels to the right as shown.
In which directions does point P move?
Up & down
Left & right
Right only
Left only

4. Reading graphs of waves

5. Displacement vs. Position graphs
Amplitude is the same
Crest to crest = wavelength

6. Displacement vs. Time graphs
Amplitude is the same
Crest to crest = period

7. Longitudinal waves – Pressure vs. Distance
Pressure = force per area = 𝐹 𝐴
Amplitude is the same
Compression to compression = wavelength

8. Check Your Understanding
What is the amplitude, period & frequency of the wave below?

9. Sound & Light
Electromagnetic waves are light waves

10. Amplitude Loudness Smaller amplitude = less energy = quieter
Sound
Light
Loudness
Smaller amplitude = less energy = quieter
Larger amplitude = more energy = louder
Brightness
Smaller amplitude = less energy = dim
Larger amplitude = more energy = bright

11. Frequency Pitch Lower frequency = lower pitch
Sound
Light
Pitch
Lower frequency = lower pitch
Higher frequency = higher pitch
“Color”
Low frequency = red
High frequency = purple

12. The Electromagnetic Spectrum

13. Use this to fill in your EM spectrum
Use this to fill in your EM spectrum. Sketch a wave with small wavelengths on the left & large ones on the right.

14. Review for Understanding
An increase in what wave property would increase the volume of a sound?
Wavelength
Speed
Amplitude
Frequency
A decrease in what wave property would make a light redder?
Wavelength
Speed
Amplitude
Frequency
*BONUS: what would you increase to make the light redder?

15. Superposition

16. Interference
Occurs when two waves meet while traveling along the same medium
Causes the medium to take on a shape that results from the net effect of the two individual waves upon the particles of the medium
Consider two pulses of the same amplitude traveling in different directions along the same medium; each displaced upward 1 unit at its crest and has the shape of a sine wave
When they are completely overlapped, the resulting shape of the medium would be an upward displaced pulse with an amplitude of 2 units.

17. Constructive Interference
A type of interference that occurs at any location along the medium where the two interfering waves have a displacement in the same direction.
Upward or downward

18. Destructive Interference
Occurs at any location along the medium where the two interfering waves have a displacement in the opposite direction
Only momentary
Equal amplitudes not necessary

19. The Principle of Superposition
When two waves interfere, the resulting displacement of the medium at any location is the algebraic sum of the displacements of the individual waves at that same location.

20. Check Your Understanding
Two pulses with amplitudes of 5 units and 2 units move towards each other on a stretched string as shown: If the pulses have the same speed and are the same distance from point P, which diagram best shows the resultant pulse when both pulses meet at point P?

21. Superposition Can Create Standing Waves
Produced as the result of the repeated interference of two waves of identical frequency while moving in opposite directions along the same medium
All standing wave patterns consist of nodes and antinodes.
Nodes - points of no desplacement
Anti-nodes - points along the medium which oscillate back and forth between a large positive displacement and a large negative displacement
Check out this gif

22. Superposition Can Create Standing Waves
The distance from one node to the next if half a wavelength; 𝑑= λ 2
The distance from one node to the next antinode is one quarter of a wavelength 𝑑= λ 4
Open ends of pipes have antinodes (air particles can move a lot)
Closed ends have antinodes (particles of the material can’t move)
Harmonics

23. Check Your Understanding
Several positions along the medium are labeled with a letter. Categorize each labeled position along the medium as being a position where either constructive or destructive interference occurs.

24. “Oh, I’m not a zebra. I’m the Doppler Effect.

25. Sheldon Cooper explains the Doppler Effect
Click the photo for a link to Sheldon’s explanation.

26. The Doppler Effect
The effect produced by a moving source of waves in which there is an apparent upward shift in frequency for observers towards whom the source is approaching and an apparent downward shift in frequency for observers from whom the source is receding.

27. Astronomical Implications
Astronomers use the information about the shift in frequency of electromagnetic waves produced by moving stars in our galaxy and beyond in order to derive information about those stars and galaxies.
The belief that the universe is expanding is based in part upon observations of electromagnetic waves emitted by stars in distant galaxies.
Galaxies are clusters of stars that typically rotate about some center of mass point. Electromagnetic radiation emitted by such stars in a distant galaxy would appear to be shifted downward in frequency (a red shift) if the star is rotating in its cluster in a direction that is away from the Earth. On the other hand, there is an upward shift in frequency (a blue shift) of such observed radiation if the star is rotating in a direction that is towards the Earth.

28. Check Your Understanding
A student starts across the crosswalk as their teacher is driving towards them. The teacher honks a warning. Compared to what the teacher hears, to the student, the pitch of the horn is:
A. The same
B. Lower
C. Higher
D. There’s no way to tell