Question

A screw gauge has a screw having $2$ threads in $1mm$. The circular scale has $50$ divisions. Find the diameter of wire, if the main scale shows $6^{th}$ division and the vernier reads $46$

• A. $6.46mm$
• B. $3.46mm$
• C. $6.54mm$
• D. $3.04mm$

Answer 1

Answer: (A)

$6.46mm$

$\begin{array}{cc}2\text{threads}& \iff 2\text{rotations}\\ & \iff 1mm\\ \text{pitch}& =\frac{1}{2}=0.5mm\end{array}$

$\begin{array}{cc}\text{Least Count =}& \frac{pitch}{\text{no of div on}C\cdot S}\\ =& \frac{0.5}{50}\\ =& 0.01mm\end{array}$

$\begin{array}{cc}\text{Final reading}& =MSR+CSR\\ & =6+46\times 0.01\\ & =6.46mm\end{array}$