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To determine the Young modulus of a wire, several measurements are taken. In which row can the measurement not be taken directly with the stated apparatus?

1. measurement: area of cross-section of wire apparatus : micrometer screw gauge
2. measurement: extension of wire ; apparatus: vernier scale
3. measurement: mass of load applied to wire ; apparatus : electronic balance
4. measurement: original length of wire ; apparatus metre rule

Correct answer: measurement: area of cross-section of wire apparatus : micrometer screw gauge

Solution

A micrometer screw gauge measures the wire’s diameter, not its cross-sectional area directly. The area must be calculated from the diameter using the formula for a circle.

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