Question

Why focal length for converging lens is negative

Answer 1

Answer:

it is because of the sign convention

if the mirror is concave then it will be negative because its reflecting surface is in negative side and its opposite is the convex mirror . this is same in lenses also

hope you understand

Answer 2

The concave mirror is converging in nature and according to the sign convention , everything lying to the left of the mirror is negative. As the focal length of concave mirror lies to the left of the mirror it has a negative sign.

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