GATE 2021 CE (CE2) – Question 31
A Shelby sampler has internal diameter 48 mm and external diameter 52 mm. Find area ratio in percent to two decimals.
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Correct answer: 17.25 to 17.45
Explanation
Area ratio measures displaced annular area relative to sampled area: $A_r=100(d_o^2-d_i^2)/d_i^2$. Substitution gives $100(52^2-48^2)/48^2=17.36111\%$. **Answer: 17.36%.** Using outside area in the denominator would use the wrong definition.