Wave Interference and Superposition: Exploring Pulse Movement

1. Answer the following… • 17. What happens to the amplitude of a pulse as it travels down the slinky and back? • 18. What happens to the speed of a pulse as it travels down the slinky and back? • 19. What do you observe about a pulse after it reaches the end of the medium that is fixed in place? • 20. What do you observe about a pulse after it reaches the end of a medium that is free to move? • 21. What would happen to a wave pulse on a spring if it encountered a new spring with different characteristics?

2. When a pulse encounters a medium boundary 2 things happen… Reflection • Some energy of the wave pulse is bounced back into the original medium. Transmission • Some energy of the wave pulse passes through the boundary into the new medium

3. Fixed End Reflection • At a fixed boundary, waves are inverted as they are reflected.

4. Free End Reflection • At a free boundary, waves are reflected on the same side of equilibrium

5. TransmissionIf the wave pulse goes from… Low density  High density medium • Reflected pulse is inverted • Transmitted pulse is upright High density  Low density medium • Reflected pulse is upright • Transmitted pulse is upright

6. What happens when wave pulses move through a medium at the same time?

7. What happens when wave pulses move through a medium at the same time? • When this occurs, waves are said to experience interference

8. Wave Interference is described by the Superposition Principle…

9. Wave Interference is described by the Superposition Principle… • Wave pulses (energy) pass through each other completely unaffected

10. Wave Interference is described by the Superposition Principle… • Wave pulses (energy) pass through each other completely unaffected • The medium will be displaced an amount equal to the vector sum of what the waves would have done individually • This results in two different types of interference: constructive and destructive

11. Constructive Interference • Pulses must meet when on the same side of equilibrium. • The resultant displacement of the medium greater than both originals

12. Destructive Interference • Pulses must meet when on opposite sides of equilibrium. • The resultant displacement of the medium is less than at least one original

13. http://www.animations.physics.unsw.edu.au/jw/waves_superposition_reflection.htm#superpositionhttp://www.animations.physics.unsw.edu.au/jw/waves_superposition_reflection.htm#superposition

14. Standing Waves • An interference pattern that results when two waves of the same frequency, wavelength, and amplitude travel in opposite directions and interfere.

15. Standing wave parts • Node – point that maintains zero displacement, complete destructive interference • Antinode – point at which largest displacement occurs, constructive interference

16. Standing waves • Only specific frequency-wavelength combinations will produce standing wave patterns in a given medium.

17. From the standing wave lab… • Frequency and wavelength are inversely proportional for a wave in a given medium. v = f v – velocity of wave (constant for a given medium) f – frequency of the wave, # of waves per second  – wavelength, how far the wave travels in a single period • Remember that f = 1/T, so the equation above could also be written as