An object is placed on the principal axis of a concave mirror at a distance of 1.5f (f is the focal length). The image will be:
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Question

An object is placed on the principal axis of a concave mirror at a distance of 1.5f (f is the focal length). The image will be:

G1 Physics · Accepted Answer

Step 1: For the concave mirror, take signed f = −F and object distance u = −1.5F. Step 2: Mirror equation 1/f = 1/u + 1/v gives 1/v = −1/F + 1/(1.5F) = −1/(3F). Step 3: Thus v = −3F, a real image in front of mirror. Final answer: (A) −3f, where f in the printed options denotes focal-length magnitude.