Question

why focus is negative in concave mirror when the object is placed between P and F​

Answer 1

Answer:

Because we take pole as original not focus

Explanation: focus lies left side of p(origin) which is at negative X axis

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Answer 2

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.