Answer the following in your openers…

• 11. What happens to the amplitude of a pulse as it travels down the slinky and back?

• 12. What happens to the speed of a pulse as it travels down the slinky and back?

• 13. What have you observed about a pulse after it reaches the end of the medium that is fixed in place (like when held by someone’s hand)?

• 14. What do you think would happen to a pulse after it reached the end of a medium that is free to move?

• 15. 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 is 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 (alternating constructive and destructive) that results when incident wave pulses encounter reflected pulses traveling the opposite way through the medium

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.

Relationship between frequency and wavelength

Wavelength vs. Frequency Wavelength vs. 1/Frequency

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)

– wavelength, length of a single wave cycle also how

far the wave travels in a single period

f – frequency of the wave

Frequency and Period

Frequency – “how often” wave cycles occur- # of cycles per unit of time- 1 Hertz (Hz) = 1 cycle per second

Period – time it takes to complete 1 wave cycle

Frequency and period are inverses of each other…f = 1/T or T = 1/f