Physics 114
Spring (12) 2006
Fundamentals of Physics II: Problem Set #9
Wave Nature of Light and Exam Review
λn = λ/n ;
sinθ = mλ/d (multi-slit maxima)
;
sinθ = mλ/w (single-slit minima)
sinθ ≈ tanθ = x/L for x<<L
Due: Wednesday Mar. 15 in class
Note: Exam 2 is the Friday after spring break (3/17). This exam will cover material through chapter
24, section 6 (with an emphasis on chapters 20-24). The exam will consist of a number of
"ConcepTest"-like problems and a few real calculation problems. The exam is closed book, closed
notes but you may bring in one-half of an 8.5x11" sheet of paper with handwritten notes and
equations. This problem set should serve as a partial review and practice. I will hold a review
session Thursday evening (3/16) from 7-9(?) to go over these problems and answer any questions.
Reading assignment: for Monday,
24.3-24.7 (interference and diffraction)
for Wednesday, 24.8-24.10 (thin film interference and polarization)
Problem assignment:
24.4 (2-slit diffraction with a He-Ne laser)
24.7 (another 2-slit diffraction experiment)
24.19 (a single slit experiment)
24.25 (changing wavelength in a single slit experiment)
24.37 (calibrating a diffraction grating with a He-Ne laser)
Bonus: 24.66 (interference effects for a radio transmitter)
power
plant
1
2
3
home
A1) A typical electrical power distribution system is shown above. The power-plant generators
operate at 20 kV. Transformer 1 increases this voltage to 350 kV for long distance transmission
on high voltage power lines. This power comes into the local electrical grid at a power substation
where transformer 2 reduces the voltage to 4 kV for local distribution. Finally, transformer 3
located on a telephone pole reduces the voltage to 240 V for household use.
a) For each of the three transformers determine the ratio Nin/Nout where Nin refers to the
number of turns on the input (left in above picture) side of the transformer.
b) Determine the current needed in the local power lines in order to deliver 20 A of current to
the house. (Assume lossless transformers and power lines).
– over –
Physics 114
Spring (12) 2006
B-field out of page
v
L
A2) The above figure shows a conducting rod, of length L and resistance R, sliding to the right at
constant speed v along a pair of frictionless metal rails. The rails have zero resistance. A uniform
magnetic field B points up out of the page and thus a current is induced in the rod.
a) What is the direction (up or down the page) of the induced current in the rod?
b) What is the magnitude of the induced current?
c) How much energy must be supplied to keep the rod moving at a constant speed v?
d) Now assume the rod is initially at rest (v=0) and the magnetic field is slowly turned off.
Describe what happens ... in particular, does the rod begin to move and, if so, in what direction?
A3) Consider a converging lens with a focal length of ƒ = 5.0 cm.
a) Determine the object location required to achieve a magnification of M = +3.
b) Determine the location of the magnified image and identify whether the image is real or virtual.
c) Sketch a ray diagram, which includes object, image, and two principle rays, for the above
situation. Show clearly how the principle rays are used to "construct" the image.