A concave mirror and convex lens are immersed in water. What change, if any, do you expect in the focal length of the two.

When a concave mirror and a convex lens are immersed in water, their focal lengths will be affected due to the change in the refractive index of the medium. In this case, water has a higher refractive index than air.

Concave Mirror:

The focal length of a concave mirror immersed in water will become shorter compared to when it is in air. This is because the refractive index of water is greater than that of air (n_water > n_air). When light passes from a medium with a lower refractive index (air) to a medium with a higher refractive index (water), it bends towards the normal. As a result, the effective path of light rays inside the concave mirror is reduced, causing the focal point to shift closer to the mirror's surface. Therefore, the focal length of the concave mirror will decrease when it is in water.
Convex Lens:

The focal length of a convex lens immersed in water will also become shorter compared to when it is in air. Similar to the concave mirror, the refractive index of water is greater than that of air, so light passing through the lens from air to water will bend more towards the normal, reducing the effective path of light rays within the lens. This causes the focal point to shift closer to the lens, resulting in a shorter focal length when the lens is in water.
In summary, when both a concave mirror and a convex lens are immersed in water, their focal lengths will decrease due to the increased refractive index of water compared to air. This change in focal length is a result of the bending of light as it passes through the different media.