Question

The diagram below shows an aquarium with four typical optical devices submerged in some liquid that has a higher index of refraction than glass. Each optical device is labeled.
Which of the optical devices will converge light when submerged in this liquid?

• A. The concave mirror and the convex lens
• B. The convex mirror and the concave lens
• C. The concave mirror and the concave lens
• D. The convex mirror and the convex lens
• E. All of the pictured optical devices converge light under water

Answer 1

The correct option is A The concave mirror and the convex lens

Concave mirror would always converge light incident of it.

But for lens, the formula of focal length is

$\frac{1}{f}=(\frac{n_{material}}{n_{medium}}-1)\left(\frac{2}{R}\right)$

Hence for $n_{mateial}<n_{medium}$, $f$ is positive for negative $R$.

Hence concave lens is converging.