Question

A slide projector is to project a $(35mm\times 23mm)$ slide on a $2m\times 2m$ screen. Find the focal length of the lens used if screen is 10 m away from the lens.

• A. 15.1 cm
• B. 17.2 cm
• C. 16.1 cm
• D. 18.2 cm

Answer 1

Answer: (B)

17.2 cm

$m=\frac{200}{3.5}=\frac{10}{u}oru=\frac{7}{40}m;$

$Using,\frac{1}{v}-\frac{1}{u}=\frac{1}{f}\frac{1}{f}=\frac{1}{10}+\frac{40}{7}orf=17.2cm$