Answer
a. 14.8 cm.
b. 1.44 m by 2.16 m.
Work Step by Step
a. Use the lens equation.
$$\frac{1}{s}+\frac{1}{s’}=\frac{1}{f}$$
$$\frac{1}{15.0cm}+\frac{1}{900cm}=\frac{1}{f}$$
$$f=14.75cm$$
b. Calculate the magnification.
$$m=-\frac{s’}{s}=-\frac{900cm}{15.0cm}=-60$$
Find the minimum dimensions of the screen.
$$|y’_1|=|m||y_1|=(60)(24mm)=1440mm$$
$$|y’_2|=|m||y_2|=(60)(36mm)=2160mm$$
