Question

derive the formula of reflection for a thin lens .on the basis of formula prove that the focal length of a concave lens is negative​

Answer 1

Answer:

Thin lens = concave lens or convex lens.

formula = 1/f = 1/v - 1/u

where f is the focal length of the mirror

v is the image distance from the mirror

u is the object distance from the mirror.

now, we know that image formed by a concave mirror is always virtual and is on the side of the object and hence has a negative distance from the mirror (-v)

so , 1/f = 1/(-v) - 1/u

=> 1/f = (-1/v) - (1/u)

=> 1/f = -u-v/vu

=> 1/f = -(u+v)/vu

=> f = -(vu/u+v)

hence the focal of a concave lens is negative.

hope it helped :)