For the homemade Vernier shown, the two identical inclined scales make angle θ. If ℓ is the scale length indicated in the figure, which expression gives the least count? Image
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Question

For the homemade Vernier shown, the two identical inclined scales make angle θ. If ℓ is the scale length indicated in the figure, which expression gives the least count? Image

G1 Physics · Accepted Answer

The projected spacing of one inclined division differs from the corresponding main-scale spacing by the Vernier constant. From the geometry in the figure the difference is ℓ[(1−cosθ)/cosθ]. Correct answer: A.