Download PHYS112 - Physics

PHYS112
Midterm Exam-II-A
May 14, 2002
Put your name, section number, and Version A or B exam taking on the blue books.
This exam consists of a section of multiple-choice questions and a section containing two
long problems; for multiple-choice questions, only answer counts. NO partial credit here.
For the two problems, partial credit will be given, if work is shown in the blue book.
Include units to answers to get full credit.
Total pts: 100.
I. Multiple-choice questions (30 pts total; 5 pts each)
1. The critical angle for the total internal reflection of a diamond-air interface (the
index of refraction for diamond is 2.419) is:
(a) 0.427  (b) 24.4 radian (c) 10.6  (d) 24.4  (e) none of the above.
2. An object is placed 10 cm in front of a convex mirror of radius 40 cm. The
image is:
(a) virtual and upright (b) virtual and inverted (c) real and upright (d) real and
inverted (e) none of the above.
3. A thin planoconcave lens (n=1.5) is formed of glass of n = 1.500 for light of
wavelength 500 nm. The radius of curvature of the spherical surface is 20 cm.
The focal length of the lens (in cm) is:
(a) +20 (b) –20 (c) – 50 (d) + 50 (e) none of the above.
4. A converging glass lens (n= 1.52) has a focal length of 74 cm in water, which
has an index of refraction of 1.33. It focal length in air (in cm) would then be:
(a) 10 (b) 20 (c) 30 (d) 40 (e) none of the above.
5. Two thin lenses are put in contact with each other; one has a focal length of
f1 = 10 cm, the other has focal length f2 = 20 cm. Considering this set of
lenses effectively as one thin lens. The image of an object located at 20 cm
from this compound lens is formed at a distance of q cm from it. The q is:
(a) 20 (b) 15 (c) 10 (d) 20/3 (e) none of the above.
6. A lens of focal length f = 20 cm is used as a magnifying glass to examine the
fine print of a legal document. The largest angular magnification that can be
obtained using this lens is:
(a) 3.35 (b) 2.25 (c) 1.45 (d) 1.25 (e) none of the above.
Problem II (30 pts)
A light ray enters a rectangular block of plastic at an angle of 1 = 45  and
emerges at an angle 2 = 76  as shown in the figure.
(a) Determine the index of refraction for the plastic.
(b) If the light ray enters the plastic at a point L = 50 cm from the bottom edge,
how long (in nanosec) does it take the light ray to travel through the plastic?
Problem III (40 pts)
A biconvex lens made of glass of refractive index n = 1.50 has equal radii of
curvature.
(a) If the focal length of the thin lens is 10 cm, find the magnitude of the two
equal radii of curvature.
An object (the arrow) 2 cm high is placed 15 cm to the left of the lens
(b) Find the location of the image produced by the lens.
(c) What is the size of the image? Is the image real? Is it upright?
(d) Draw a ray diagram (at least two rays) to show how the image could be
formed by this lens.
A concave mirror of focal length 15 cm is now placed 20 cm to the right of the
lens. The image from the lens now becomes the object for the mirror.
(e) Find the location of the final image of the object produced by the mirror.
(f) What is the size of this final image? Is it real? Is it upright?
(g) Draw a ray diagram (at least 2 rays) showing how the final image is formed
by the mirror.