Question

A micrometre screw gauge has a negative zero error of $0.0018cm$. The main scale reading is $3.6cm$ for an object. The baseline coincides with the ${45}^{th}$ division of the circular scale. Calculate the true length of the object in $cm$.

• A. $7.2126cm$
• B. $3.6063cm$
• C. $36.063cm$
• D. $0.7212cm$

Answer 1

The correct option is B $3.6063cm$

Given:
Negative zero error, $E=-0.0018cm$
Main scale reading, MSR $=3.6cm$
The circular scale division coinciding with the baseline, $p=45$
Least count of a micrometre screw gauge, L.C. $=1\mu m=0.001mm=0.0001cm$
Observed length = MSR + (p $\times$ L.C.) = $3.6+(45\times 0.0001cm)=3.6045cm$
True length = Observed length - Negative zero error
= $3.6045-(-0.0018)$
= $3.6063cm$