Question

A concave mirror has a focal length of 2 metre in vacuum. What would be its focal length when used in a medium of refractive index 2.759?

• A. $2m$
• B. $2\times 2.759$
• C. $\frac{2}{2.759}m$
• D. 3.3 m

Answer 1

Answer: (A)

$2m$

The Focal length of concave/convex/ plane mirrors does not change when medium changes.this is because the focal length of the mirror does not depend on the external medium in which it is held.