In Searle's experiment, adding a 50 kg load to a 3 m wire requires a quarter turn of a micrometer screw of pitch 1 mm to restore the spirit level. The wire cross-sectional area is 10⁻⁵ m². Find Young's modulus.
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Question

In Searle's experiment, adding a 50 kg load to a 3 m wire requires a quarter turn of a micrometer screw of pitch 1 mm to restore the spirit level. The wire cross-sectional area is 10⁻⁵ m². Find Young's modulus.

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G1 Physics · Accepted Answer

Quarter turn of pitch 1 mm gives extension ΔL=0.25 mm=2.5×10⁻⁴ m. Load force≈50×10=500 N. Y=FL/(AΔL)=500×3/(10⁻⁵×2.5×10⁻⁴)=6×10¹¹ N m⁻². Correct answer: A.