Question

In a Screw Gauge, the fifth division of the circular scale coincides with the reference line when the ratchet is closed. There are 50 divisions on the circular scale, and the main scale moves by 0.5 mm on a complete rotation. For a particular observation, the reading on the main scale is 5 mm and the 20^th division of the circular scale coincides with the reference line. Calculate the true reading.

Options

• 5.00 mm

• 5.20 mm

• 5.15 mm

• 5.25 mm

Answer 1

5.15 mm

Explanation:

Least count = `0.5/50`

In this case, the fifth division coincides with the reference line.

This is a positive zero error case because zero error is always subtracted from the observed reading to get the actual reading.

True Reading = Observed - Zero Error

Observed Reading = 5 + L.C. × 20 - L.C × 5

= `5 + 0.5/50 xx 20 - 0.5/50 xx 5`

= 5.15 mm