If a convex lens having focal length f and refractive index 1.5 is immersed in water then new focal length will be $(μ_w = 4/3)$
Answer & explanation
Correct answer: option 4
$\frac{1}{f}=(μ_g-1)(\frac{1}{R_1}-\frac{1}{R_1})$ . . . (1)
$\frac{1}{f_w}=(\frac{μ_g-μ_w}{μ_w})(\frac{1}{R_1}-\frac{1}{R_1})$ . . . (2)
$⇒f_w=4f$