When the refractive index of medium is greater than the lens then what will happen to the focal length of the lens?
[Physics] Refractive index and focal length
lensesopticsrefraction
lensesopticsrefraction
When the refractive index of medium is greater than the lens then what will happen to the focal length of the lens?
Best Answer
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.