Question

The number of circular divisions of shown screw gauge are 50. It moves 0.5 mm on main scale in one rotation. The diameter of the ball is:

• A. 2.25 mm
• B. 2.20 mm
• C. 1.20 mm
• D. 1.25 mm

Answer 1

The correct option is C 1.20 mm

As shown in first figure the zero error of the screw gauge is:

$ZE=\frac{5\times 0.5}{50}=0.05mm$
Least count of circular scale $=\frac{0.5}{50}=0.01mm$
Circular scale reading $=25\times 0.01=0.25mm$
Main scale reading $=2\times 0.5=1mm$
Actual measurement is $=MSR+CSR$ $-$ ZE $=1+0.25-0.05=1.20mm$