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?
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
Fixed End Reflection At a fixed boundary, waves are inverted as they are reflected.
Free End Reflection At a free boundary, waves are reflected on the same side of equilibrium
Transmission If 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
What happens when wave pulses move through a medium at the same time?
What happens when wave pulses move through a medium at the same time? When this occurs, waves are said to experience interference
Wave Interference is described by the Superposition Principle…
Wave Interference is described by the Superposition Principle… Wave pulses (energy) pass through each other completely unaffected
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
Constructive Interference Pulses must meet when on the same side of equilibrium. The resultant displacement of the medium greater than both originals
Destructive Interference Pulses must meet when on opposite sides of equilibrium. The resultant displacement of the medium is less than at least one original
http://www. animations. physics. unsw. edu http://www.animations.physics.unsw.edu.au/jw/waves_superposition_reflection.htm#superposition
Standing Waves An interference pattern that results when two waves of the same frequency, wavelength, and amplitude travel in opposite directions and interfere.
Standing wave parts Node – point that maintains zero displacement, complete destructive interference Antinode – point at which largest displacement occurs, constructive interference
Standing waves Only specific frequency-wavelength combinations will produce standing wave patterns in a given medium.
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 𝒗= 𝝀 𝑻