The focal length of a concave mirror is f when placed in air. What will be its focal length if it's placed in water having the refractive index of $\frac{4}{3}$ ?

• When a beam of parallel rays is incident on a concave mirror, rays meet at focus after reflection and the distance between the pole and the focus is called the focal length.
• When concave mirrors are immersed in water, the focal length of the mirrors does not change as a reflection does not get affected when the medium is changed.

Therefore, the focal length of the concave mirror will be f in water as well.