GATE 2017 ME (ME1) – Question 60

Metrology and Inspection · Linear and angular measurements, comparators · 2 marks · Multiple choice

The surface-roughness profile is triangular as shown, with peak-to-valley height 20 μm. Find the centre-line average roughness $R_a$ in μm.

Diagram for GATE 2017 ME (ME1) question 60

5
6.67
10
20

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Show answer and explanation

Correct answer: (A) 5

Explanation

The mean line lies halfway between peak and valley, so the maximum absolute departure is 10 μm. Over a linear triangular period, the area between profile and mean line equals the period length times half this amplitude. Therefore $R_a=10/2=5$ μm, A. The half-height 10 μm is not the average absolute deviation.

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