-Waves at Boundaries

-Reflection

-Interference of Waves

Physics

Mrs. CoyleCoyle, Greece, 2009, Island of Antipaxos

How is the speed of a wave affected when a wave enters

from one medium to another?• The speed depends on the medium.

• It does not depend on frequency and amplitude.

• It remains constant in a given medium at the same conditions.

• When a wave enters a different medium, its speed changes but its frequency remains the same.

Speed of a Wave, v =f• For a given medium, v=constant.

What does a high or low amplitude indicate?

Low Amplitude High Amplitude

What happens when a wave reaches a boundary?

• Part of the incident wave is transmitted and part of it is reflected.

Pulse travelling from less dense to more dense medium.

• What happens to the pulse at the interface?

http://www.dacc.edu/~qchen/P102/labs/LAB5.HTM

Reflection of a Pulse from a Fixed End

What is the

direction of the

reflected

pulse?

http://www.dacc.edu/~qchen/P102/labs/LAB5.HTM

Reflection of a Wave

from a Fixed End:

the pulse returns inverted

http://openlearn.open.ac.uk/file.php/3524/TA212_2_008i.jpg

Reflection of a Pulse from a Free End

What is the

direction of the

reflected

pulse?

http://www.dacc.edu/~qchen/P102/labs/LAB5.HTM

Wave on a String

• (Applet) http://phet.colorado.edu/sims/wave-on-a-string/wave-on-a-string_en.html

Interference

• When two pulses pass the same point at the same time the waves superimpose either constructively or destructively.

– Constructive Interference– Destructive Interference

Constructive Interference: resulting wave has a greater

amplitude.

Destructive Interference: Resulting wave has a smaller

amplitude.

• The displacements

are added algebraically at the given point in time.

Interference

http://ircamera.as.arizona.edu/NatSci102/NatSci102/movies/interference.gif

Superposition

• Simulation:

Constructive and Destructive Interference (string with loose or fixed end)

• http://www3.interscience.wiley.com:8100/legacy/college/halliday/0471320005/simulations6e/index.htm?newwindow=true

One Wave Two Waves Interfering

Interference in Water Waves