The pitch of the screw guage is $1 \mathrm{~mm}$ and there are 100 divisions on the circular scale. When nothing is put in between the jaws, the zero of the circular scale lines 8 divisions below the reference line. When a wire is placed between the jaws, the first linear scale division is clearly visible while $72^{\text {nd }}$ division on circular scale coincides with the reference line. The radius of the wire is :
Correct Option: , 3
(3)
Least count. $=\frac{\text { pitch }}{\text { no. of div. }}=\frac{1 \mathrm{~mm}}{100}=0.01 \mathrm{~m}$
+ve error $=8 \times$ L. C. $=+0.08 \mathrm{~mm}$
measured reading $=1 \mathrm{~mm}+72 \times$ L. C.
$=1 \mathrm{~mm}+0.72 \mathrm{~mm}$
$=1.72 \mathrm{~mm}$
True reading $=1.72-0.08$
$=1.64 \mathrm{~mm}$
Radius $=\frac{1.64}{2}=0.82 \mathrm{~mm}$
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