GATE 2026 PI – Question 54
A 2D stylus profilometer measures a 0.8 mm surface profile. The graph uses vertical magnification 10000 and horizontal magnification 100. Areas recorded above the datum are 140,60,150,50 mm², and below it 70,50,120,160 mm². Find average roughness R_a (µm, two decimals).
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Correct answer: 1 to 1
Explanation
The total absolute graph area is 400 + 400 = 800 mm². Correct both magnifications to get actual area $800/(10000\cdot100)=0.0008$ mm². Divide by actual sampling length: $R_a=0.0008/0.8=0.001$ mm = **1.00 µm**.