Question

focal length of a concave lens is considered to be​

Answer 1

Answer:

actuality, there are two focal points for every lens, the same distance from the lens, on opposite sides. The distance from the lens to the focal point is called the focal length. For converging lenses, the focal length is always positive, while diverging lenses always have negative focal lengths.

Answer 2

The focal length of a concave mirror is negative and that of a convex mirror is positive. You can also prove the same by using the mirror formula (1/f = 1/v +1/u). Let's see how, Since we know object is always placed on the left side or direction opposite to the incidence ray of the mirror.

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