Transcript CH 8: Magnetic Fields

CH 9: Waves and Light
9.3 – Diffraction and Interference of Water
Waves
Agenda
Hand in Trip Forms/Money
 Hand in pg. 409 #10 research assignment
 Complete the index cards for students who were
away

Warm up on Section 9.2
 Complete Section 9.3


Textbook questions
Learning Goals

Describe and explain the diffraction and
interference of water waves in two
dimensions

Conduct inquiries involving the
diffraction and interference of waves,
using ripple tanks or computer
simulations
Warm Up
A 10.0-Hz water wave travels from deep
water, where its speed is 38.0 cm/s, to
shallow water, where its speed is 28.0
cm/s and θi = 30°. Find (a) the relative
index of refraction, (b) the wavelengths
in the two media, and (c) the angle of
refraction in the shallow water.
Diffraction


w

1

w
1
Review of Interference

When two waves meet their amplitudes
add (like adding functions)
 Constructive Interference: New amplitude is
larger
 Destructive Interference: New amplitude is
smaller

Nodes are locations of complete
destructive interference
Two Point Source Interference

A point Pn is on the nth nodal line created by two
sources at S1 and S2 if:
 1 
Pn S1  Pn S2  n  
 2 

If S1 and S2 are a distance d apart and Pn is far from
the sources then:
 1 

sin  n  
n


2 d
Where n is measured from the right bisector of S1S2
Two Point Source Interference

Again, if Pn is far from S1 and S2
x n  1 
 n  
L  2 d


Where xn is the perpendicular distance
from the right bisector of S1S2 and L
distance from Pn to the midpoint of S1S2
Question

An interference pattern is set up by two
point sources of the same frequency,
vibrating in phase. A point on the second
nodal line is 25.0 cm from one source,
29.5 cm from the other. The speed of
the waves is 7.5 cm/s. Calculate the
wavelength and the frequency of the
sources.
Light: Wave or Particle?

http://www.youtube.com/watch?v=DfPep
rQ7oGc
Wave/Particle Duality
Part 1
 http://www.youtube.com/watch?v=Q_h4I
oPJXZ

Part 2
 http://www.youtube.com/watch?v=_riIYv2Ym8

Homework
Homework pg. 469 #3-7
Work on your Presentations for
Wednesday