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

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

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…

1. Wave pulses (energy) pass through each other completely unaffected

Wave Interference is described by the Superposition Principle…

1. Wave pulses (energy) pass through each other completely unaffected

2. 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.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 = fv – 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