PHYS-222 Worksheet 13 for Section 25 & 36
TA: Yang Li, leeyoung@iastate.edu
November 9, 2012
Problem 13-1
Complete the principal rays a, b, c after reflection. There is a 4th principal ray. Show it on the diagram.
Problem 13-2 (pay attention to signs)
a. A convex mirror has a radius curvature 1 m. A 20 cm tall kitty looks like only 15 cm. Where is the
kitty in front of the mirror?
s = 16.67cm, s0 = −12.5cm
b∗ . A concave mirror has a radius of curvature 1 m. A kitty sits in front of it. If the image of the kitty is
30 cm away from it. What is the lateral magnification m? (hint: the image could be in front or behind,
could be real image or virtual )
s1 = 12.7985cm, s2 = 117.202cm, s3 = 87.2015cm, s4 = −12.7985cm
s01 = −17.2015cm, s02 = 87.2015cm, s03 = 117.202cm, s04 = 12.7985cm.
m1 = 1.34403, m2 = −0.744031, m3 = −1.34403, m4 = 0.744031
Useful formulae:
R
,
“+” for concave mirrors, “-” for convex mirrors
2
1
1
1
+
=
note that for virtual image, di is a negative number
do
di
f
hi
di
m=
=−
negative magnification means inverted image
ho
do
√
−b ± b2 − 4ac
ax2 + bx + c = 0, the roots are: x =
2a
f =±
1