Question

A convex lens of glass $(\mu=1.5)$ has a focal length of $8\, cm$ when placed in air. What is the focal length of lens when it is immersed in water $\left(\mu=\frac{4}{3}\right) ?$

• A. 4 cm
• B. 8 cm
• C. 16 cm
• D. 32 cm

Answer 1

Answer: (D)

32 cm

Answer 2

$f_{\text {water }} =4 \times f_{\text {air }}$
$=4 \times 8=32\, cm$