Question

A double convex lens of glass of refraction index $\mu$ is immersed in a medium of refractive index ${\mu }_1$. If a parallel beam emerges undeviated through the lens, then:

• A. $\mu ={\mu }_1$
• B. $\mu =\frac{1}{{\mu }_1}$
• C. $\mu >{\mu }_1$
• D. $\mu <{\mu }_1$

Answer 1

Answer: (A)

$\mu ={\mu }_1$

A parallel beam of light passes through the focus of a lens. For the light to remain undeviated, focus should lie at infinity or refraction must not occur so that light does not bend. For focus to be at infinity, radius should be infinitely large in which case a double convex lens cannot be formed. For refraction to not happen, refractive index of the medium of convex lens should be same as that of the medium. Hence, option A is correct.