April 21, 2009
PHY 2054 Discussion Spring ‘09
Conceptual Review: Chapter 25
A . Cameras
1.
Relate f-number with the intensity of light.
B. Corrective Lenses
1.
A lens with a power of 2.0 diopters is in contact with a lens of -0.50 diopters. What is the power of
the combined lenses?
2. A person has a far point of 50 cm. What is the power of the contact lens required to correct the patient
vision? What is the power of the required glasses if the glasses are 1.0 cm away from the eyes?
C. Simple Magnifier
1. Why is the angular magnification useful as long as eyes are concerned?
2. What are the range of object distance to see an enlarged image with a magnifying lens and the
corresponding magnifications?
D. Microscopes & Telescopes
1. A microscope has two interchangeable objectives of focal lengths 2.0 cm and 0.4 cm. It also has two
eyepieces of focal length 2.5 cm and 5.0 cm. The objective and the eyepiece are separated by 20 cm. Find
the maximum & minimum magnification.
2. In a telescope/microscope, the image formed by an objective lens is located near the focal point of the
eyepiece. What is it for?
E. Resolutions
1. Light with a wavelength of 500 nm shines through a lens with an aperture diameter of 0.50 cm. What is
the limiting angle of resolution?
2. How many lines in a grating must be illuminated to obtain a resolving power of 800 in the 2 nd order
spectrum?
April 21, 2009
PHY 2054 Discussion – Spring ‘09
Practice Exam Problems (Chapter 25)
1. Doubling the aperture diameter of a camera lens will change the light intensity admitted to the film by
what factor? (Camera)
a. 0.2
b. 0.50
c. 2.0
d. 4.0
2. You are designing eyeglasses for someone whose near point is 60 cm. What focal length lens should
you prescribe so that an object can be clearly seen when placed at 25 cm in front of the eye? (Corrective
Lenses)
a. 15 cm b. 18 cm
c. 43 cm d. 60 cm
3. A simple magnifier makes an image appear at the near point distance from the eye of the viewer (25
cm). What is the magnifying power of the magnifier if it is constructed of a lens of focal length of 4.0
cm? (Simple Magnifier)
a. 1.2
b. 5.0
c. 7.3
d. 50
4. You are building a compound microscope with an objective lens of focal length 0.70 cm and an
eyepiece lens of focal length 5.0 cm. You mount the lenses 18 cm apart. What is the maximum
magnification of your microscope? (Microscopes)
a. 3.1 b. 7.3
c. 67
d. 130
5. A telescope has an objective lens with a focal length of 100 cm and an eyepiece of focal length 3.0 cm.
What is the angular magnification of the telescope? (Telescopes)
a. 30
b. 33
c. 60
d. 180
6. A microscope has an objective lens with an aperture of diameter 0.60 cm where a monochromatic light
source of wavelength 580 nm is used to illuminate the object. It is determined that the minimum angle of
resolution is 1.18  104 rad. If the illuminating source were replaced by an violet source of wavelength
420 nm, what would the minimum angle of resolution now become? (1 nm = 10 9 m) (Resolution) a. 1.6
 104 rad
b. 1.2  104 rad
c. 0.85  104 rad d. 0.58  104 rad
7. When using 529 nm light, how far is the adjustable mirror of a Michelson interferometer moved when
300 fringe shifts are counted? (Michelson Interferometer)
10-5 m d. 1.58 × 10-4 m
Answers: 1-d
2-c
3-c
4-d
5-b
6-c
7-b
a. 9.90 × 10-6 m b. 3.97 × 10-5 m c. 7.92 ×