Question

why the focal length of concave mirror is negative???​

Answer 1

Answer:

Since, object is always placed in front of the mirror hence the sign of object is taken as negative. Since, the centre of curvature and focus lie in front of the concave mirror, so signs of radius of curvature and focal length are taken as negative in the case of concave mirror.

Answer 2

Answer-

the focal length of a concave mirror is negative because the object is always placed on the left side of the mirror show that the direction of incident light is from left to right. Since the the incident light always goes from left to right, all the distances measured from the pole of the mirror to the right will be considered positive because they will be in the same direction as the incident light. On the other hand, all the distances are measured from pole of mirror to the left side will be negative because they are measured against the direction of incident light. The focus of concave mirror is in front of the mirror on the left side, so the focal length of a concave mirror is considered negative.

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