Question

In the laboratory, a student measures the thickness of a metal sheet using a screw gauge as shown in the figure. What is the thickness of the sheet?

• A. 7.81 mm
• B. 7.531 mm
• C. 7.31 mm
• D. 7.831 mm

Answer 1

The correct option is A

7.81 mm

First part of the measurement, main scale reading= 7.5 mm
Head scale division that coincides with the pitch scale axis, circular scale division = 31
Second part of the measurement, $\text{circular scale division}\times \text{least count}=31\times 0.01mm=0.31mm$
Measurement with zero error = Main scale reading + (Circular scale division $\times$ Least count) = 7.5 + 0.31 = 7.81 mm.