Download Quiz 5

Quiz 5
Name:
Phys224
Date:
Summer 2008
Dr. P. Hanlet
Show your work!!! If I can read it, I will give you partial
credit!!! Correct answers without work will NOT get full credit.
Concept (3 points)
1. In your own words, what is Huygen’s Principle?
Huygen’s Principle states that all points on a wave front serve as point
sources of spherical secondary wavelets. After a time t, the new position
of the wavefront will be that of a surface tangent to these secondary
wavelets.
2. Draw the intensity vs angle diagram look like for a single-slit diffraction pattern, if the first minima
is at 15◦ and the second minima at 25◦ .
I
35
30
25
20
15
10
5
0
1
5
10
15
20
25
30
35
θ
Problem (5 points)
3. In the figure below, sources A and B emit long-range radio waves of wavelength 400m, with the
phase of the emission from source A ahead of that from source B by 90◦ . The distance rA from A to
D is greater than the corresponding distance rB by 100m. What is the phase difference of the waves
at D?
D
rA
rB
A
B
λ
Since source A leads source B by 90◦, this means that A leads B by
4
wavelengths.
Furthermore, since the path rA is 100m longer than the path rB , then light
λ
100 m
, or wavelength.
from A will lag behind light from B by
400 m
4
λ
Finally, since the first phase difference leads by and the second lags by
4
λ
, then the sum of the two contributions at D is φ = 0.
4
2