Cycle III AP Physics
John Dewey High School
Mr. Klimetz
Problems in Geometric Optics
Solve the following problems on a separate sheet of paper or in the spaces provided. Remember to employ proper problem-solving techniques throughout, including equations, substitutions, and units. You must show all work.
Equations
Curved Mirrors, Lenses and Their Images
1/f  = 1/so + 1/si   and   f  = R/2
where f is the focal length, so is the object distance, si is the image distance and R is the radius of curvature. As such
-si/so = hi/ho = M
where hi is the image height, ho is the object height, and M is magnification. 1.  A 10-cm-tall object is placed 20 cm in front of a concave mirror with a focal length of 8 cm. Calculate the image location and its size.
2.  An object is placed in front of a converging lens in such a way that the image produced is inverted and larger. If the lens were replaced by one with a larger index of refraction, how would the size of the image change?
Numerically, negative focal lengths imply convex mirrors and concave lenses.
Real images are always inverted.
The focal length of a lens is dependent on the frequency of light used and the refractive index.
Concepts
Numerically, positive focal lengths imply concave mirrors and convex lenses.
Numerically, focal lengths are one-half the radius of curvature.
3.  You wish to make an enlarged reproduction of a document using a copying machine. When you press the enlargement feature button on the control panel, to which point does the the lens inside the machine move?
(A) Increases.
(B) Decreases.
(C) Increases or decreases depending on the degree of change.
(D) Remain the same.
(E) Increase or decrease depending on the wavelength of light.
(A) To f.
(B) To 2f.
(C) Between f and 2f.
(D) Beyond 2f.
(E) Less than f.
4.  A negative image height indicates that the image formed by a concave mirror will be
(A) Real.
(B) Erect.
(C) Inverted.
(D) Smaller.
(E) Both B and D.
5.  Real images are always produced by
(A) Plane mirrors.
(B) Convex mirrors.
(C) Concave lenses.
(D) Convex lenses.
(E) Both B and C.
6.  The focal length of a convex mirror with a radius of curvature of 8 cm is
(A) 4 cm
(B) -4 cm
(C) 8 cm
(D) -8 cm
(E) 16 cm
7.  An object is located 15 cm in front of a converging lens. An image twice as large as the object appears on the other side of the lens. The image distance must be
(A) 0.3 m
(B) 2.6 m
(C) 3.2 m
(D) 4.5 m
(E) 1.6 m