Question

The pitch of a screw gauge is `1` mm and there are `100` division on its circular scale. When nothing is put in between its jaws, the zero of the circular scale lies `4` divisions below the reference line. When a steel wire is placed between the jaws, two main scale divisions are clearly visible and `67` divisions on the circular scale are observed. the diameter of the wire is
A. `2.71mm`
B. `2.67mm`
C. `2.63mm`
D. `2.65mm`

Answer 1

Correct Answer - C
`p=1mm,N=100`
Least count `C=P/N=(1mm)/100=0.01mm`
The instrument has a positive zero error
`e=+NC=+4xx0.01=0.04mm`
Main scale reading is `2xx(1mm)=2mm`
Circular scale reading is `67(0.01)=0.67mm`
`:.` observed reading is `R_(0)=2+0.67=2.67mm`
So true reading `=R_(0)-e=2.63mm`