Question

The pitch of a screw gauge is $0.5\,mm$ and the head scale is divided in $100$ parts. What is the least count of the screw gauge?
(A) $0.5\,mm$ or $0.05\,cm$
(B) $0.05\,mm$ or $0.005\,cm$
(C) $0.005\,mm$ or $0.0005\,cm$
(D) $0.0005\,mm$ or $0.00005\,cm$

Answer 1

The screw gauge pitch is defined as the distance per revolution passed by the spindle, which is determined by rolling the head scale over the pitch scale to complete one full rotation. The formula to find least count of a screw gauge is L.C$=$pitch of a screw gauge/division of head scale

Complete step by step answer:
The least count of the screw is known as the distance moved by the screw tip when switched through one division of the head scale.
A screw gauge is generally used as a precision instrument to minimize the micro errors. It is a screw with a U-shaped frame. There is a main scale used for the measurements. There is a small cylindrical structure called thimble which is used to move the frame. There is another scale called the circular scale which is present in the thimble. A spindle and anvil are attached to the U-shaped frame.
Given,
Pitch of a screw-gauge $= 0.5\,mm$
Division of head scale $= 100$
Least count =?
We know that,Least count of a screw gauge is L.C $=$ Pitch of a screw gauge/division of head scale.
L.C $= \dfrac{{0.5}}{{100}}$
$= 0.005\,mm$ or $0.0005\,mm$
Hence, the least count of the screw gauge $= 0.005\,mm$ or $0.0005\,cm$.

Hence, option C is correct.

Note: There should be many things kept in mind while taking least count with a screw gauge. There should be zero error to get the correct measurement. The screw is rotated forward for this reason, until the screw barely reaches the anvil and the edge of the cap is on the pitch scale’s zero point. The zero in the gauge should be kept vertical.