A beam of light from a source L is incident normally on a plane mirror fixed at a certain distance x from the source. The beam is reflected back as a spot on a scale placed just above the source L. When the mirror is rotated through a small angle θ the spot of the light is found to move through a distance y on the scale. The angle θ is given by

Question

A beam of light from a source L is incident normally on a plane mirror fixed at a certain distance x from the source. The beam is reflected back as a spot on a scale placed just above the source L. When the mirror is rotated through a small angle θ the spot of the light is found to move through a distance y on the scale. The angle θ is given by

Infinity Learn · Accepted Answer

When mirror is rotated by θ angle reflected ray will be rotated by $$2$$ θ.For small angle θ $$tan2$$θ≈$$2$$θ$$=yx$$∴ θ$$=y2x$$

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