To measure a concave mirror's focal length f , an object pin lies on its principal axis at distance x . Its image is inverted. Looking along the axis from a distance, a student moves the eye left

Question

To measure a concave mirror's focal length f , an object pin lies on its principal axis at distance x . Its image is inverted. Looking along the axis from a distance, a student moves the eye left and sees the image shift to the right of the pin. Then:

TestHub · Accepted Answer

On moving the eye left, the nearer image shifts right relative to the farther object pin.

Hence the real image is farther from the mirror: $v > x$ .

$\frac{1}{f} = \frac{1}{x} + \frac{1}{v}$ .

For $v > x$ , $\frac{1}{x} < \frac{1}{f} < \frac{2}{x}$ .

Therefore $f < x < 2 f$ ; option B.

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