When a copper coin is heated through 80 deg C, its diameter increases by 0.2%. Which of the following statements is correct?

Percentage rise in the area of a face is 0.4 %
Percentage rise in the thickness is 0.4 %
Percentage rise in the volume is 0.6 %
Coefficient of linear expansion of copper is 0.25 x 10⁻⁴ per deg C

Correct answer: Coefficient of linear expansion of copper is 0.25 x 10⁻⁴ per deg C

Solution

alpha = 0.002/80 = 2.5e-5 = 0.25e-4 per deg C; thickness rises 0.2% (so the 0.4% thickness option is wrong), making the alpha statement the correct single choice.

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