1
$\begingroup$

When the refractive index of medium is greater than the lens then what will happen to the focal length of the lens?

$\endgroup$
4
$\begingroup$

The sign of the focal length will change. So, a concave lens would behave like a convex lens, and a convex lens as concave lens.

The lens maker’s formula for a thin lens is: $$\dfrac{1}{f} = \left(\dfrac{\mu_2}{\mu_1} -1\right)\left(\dfrac{1}{R _1} - \dfrac{1}{R_2}\right)$$

Where $\mu_2$ is the refractive index of the lens, and $\mu_1$ is the refractive index of the medium.

If $\mu_1 > \mu_2$, then $\frac{\mu_2}{\mu_1} -1 < 0$.

So, the focal length of a convex lens will become negative, and it will act like a concave lens, and focal lens of a concave lens will become positive, so it'll act as a convex lens.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.