L4 Transverse Waves revisited- Reflection, Interference, Standing Waves on String

L4 Transverse Waves

revisited-Reflection, Interference,

Standing Waves on String

Transverse wave propagation

Wave reflection at a fixed end:the restoring force in the

boundary material causes an upward pulse to become a

downward pulse upon reflection

Wave reflection at an open end:the upward pulse maintains its

orientation upon reflection

PhET SimulationWave on a String

Wave Interference/Wave Superposition

Ct 4.5.2.sup

The pulse on the left is moving right, the pulse on the right is moving left. What do you see at the "central moment" they pass through one another?

Ct 4.5.2.sup

C

A

B

D

E

SIMwww.physics.nyu.edu/~ts2/Animation/waves.html

Suppose the pulse reflected from a boundary and moving to the left seen earlier meets another pulse

moving to the right…

Identical waves

movingin

oppositedirections

Motionof

pointalongthe

spring

Standing wave Applet

http://webphysics.davidson.edu/Applets/superposition/default.html

(Example 2)

Standing wave representation

Standing Wavesin a Stretched String

Conditions for standing waves

Recall thatf=v/λ

Hence fn =n f1

where f1 = v/(2L)

f1 is called the fundamental frequency (the lowest possible frequency)

All harmonics (n= 1,2,3,…) are possible excitations for a string held at both ends!

f2 is called the 2nd harmonic, and is also sometimes referred to as

the 1st overtone (especially in reference to sound).

f3 is the 3d harmonic or the 2nd overtone, etc.

Recall that v=f λ.Suppose we keep v and the length of the string constant.Can we establish a standing wave if we increase the vibrating frequency from f1 to 1.2 f1?A) yes B) noC) sometimes D) Not enough information given

Standing Waves on a String (rope)Demo