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In Searle's experiment for measuring Young's modulus of elasticity of a wire, after applying each increment of load the experimenter waits for approximately two minutes before taking a reading. What is the primary reason for this waiting period?

1. So that the wire can fully elongate to its equilibrium length under the new load.
2. So that the wire temperature returns to room temperature after the strain heating.
3. So that the vertical oscillations set up in the wire by loading can die down.
4. So that there is no change in the radius of the wire.

Correct answer: So that the vertical oscillations set up in the wire by loading can die down.

Solution

Suddenly adding a load causes the wire-weight system to oscillate vertically. These oscillations must be fully damped out before the spirit-level reading is taken, otherwise the measured extension will fluctuate. Two minutes is enough time for oscillations to subside.

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