If the lens is placed in water instead of air, how does its focal length change

(i) If the lens is placed in water instead of air, how does its focal length change?

(ii) Which lens, thick or thin has greater focal length?

Answer

(i) The focal length of the lens will increase in water

(Focal length of the lens depends on the refractive index of the material of lens relative to its surrounding medium)

(ii) thinner