Physics 221: Exam 1, Spring-2011
Name:
Section. No:
NOTE: Problems 2 and 5 are each worth 18 points and the rest are each worth 16 pts
1. Two identical concave mirrors are set facing each other 1.0 m apart. A small light bulb is placed
halfway between the mirrors. A small piece of paper placed just to the left of the bulb prevents light
from the bulb from directly shining on the left mirror. A good image of the bulb appears on the left side
of the piece of paper which is almost exactly at the halvay point between the mirrors. What the focal
length of the mirrors?
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2. A diverging lens with a focal length of-14 cm is placed 12 cm to the right of a converging lens with a
focal length 18 cm. An object is placed 33 cm to the left of the converging lens.
a) Where will the fmal image be located?
b) Is it real or virtual?
c) What is the magnification?
d) Is it erect or inverted?
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3. Monochromatic light of variable wavelength is incident normally on a thin sheet of plastic film in air. The
reflected light is a maximum only for ? 491.4 mn and
688.0 nm in the visible spectrum. What is the
thickness of the film if n = 1.58? Hint: Assume successive values of m.
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4. Two polarizers are oriented at 36.0° to one another. Light polarized at an 18.00 angle to each polarizer
passes through both. What is the transmitted intensity (%)?
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5. The entrance to a boy’s bedroom consists of two doorways, each 1.0 m wide, which are separated by a
distance of 3.0 m. The boy’s mother yells at him through the two doors telling him to clean up his room. Her
voice has a frequency of 400 Hz. Later when the mother discovers the room is still a mess, the boy says he
never heard her yelling to clean his room. The velocity of sound is 340 mIs.
a) First find all the angles 0 at which no sound will be heard within the bedroom when the mother yells using
double slit interference. Assume sound is completely absorbed when it hits a wall.
b) Find all the angles where a minimum occurs for single slit diffraction
c) If the boy was at the position shown when his mother yelled, does he have a good explanation for not hearing
her?
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6. Red laser light from a He-Ne laser (X = 632.8 nm) is used to calibrate a diffraction grating. If this
light creates a second order fringe at 53.2° after passing through the grating, and light of unknown
wavelength ? creates a first-order fringe at 20.60, find A.
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