Question

A standard screw gauge has a negative error of 7 divisions. While measuring the diameter of a wire the reading on the main scale is 2 divisions. and the 72nd circular scale division coincides with the base line. If the divisions on the main scale are 10 to a centimeter and the circular scale has 100 divisions, then calculate the correct diameter?

• A. $2.74$ mm
• B. $2.79$ mm
• C. $2.35$ mm
• D. $1.53$ mm

Answer 1

The correct option is B $2.79$ mm

$\begin{array}{cc}1MSD& =\frac{1}{10}cm\\ & =0.1cm\\ \text{In this case, assuming}\text{the pitch}& =0.1cm\\ L\cdot C=& \frac{\text{pitch}}{C\cdot S\cdot D}\\ & =\frac{0.1}{100}\\ & =0.001cm\end{array}$

$\begin{array}{c}\text{zero error}\text{(-ive)}=-7\times 0.001=-0.007\end{array}$

$\begin{array}{c}\text{Final reading}=mSR+VSR-\text{zero}\text{error}\end{array}$

$=2\times 0.1+72\times 0.001+0.007$$\begin{array}{c}=0.279cm=2.79mm\end{array}$