There are 100 divisions on the circular scale of a screw gauge of pitch 1 mm. With no measuring quantity in between the jaws, the zero of the circular scale lies 5 divisions below the reference line. The diameter of a wire is then measured using this scre

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Solution

Q.
There are 100 divisions on the circular scale of a screw gauge of pitch 1 mm. With no measuring quantity in between the jaws, the zero of the circular scale lies 5 divisions below the reference line. The diameter of a wire is then measured using this screw gauge. It is found that 4 linear scale divisions are clearly visible while 60 divisions on circular scale coincide with the reference line. The diameter of the wire is [2024]

1 4.60 mm

2 3.35 mm

3 4.65 mm

4 4.55 mm

Ans.
(4)

Pitch P = 1 mm, N = 100

least count $C = \frac{P}{N} = \frac{1 mm}{100} = 0.01 mm$

The instrument has a positive zero error.

$e = N C = 5 \times 0.01 = 0.05 mm$

Main scale reading is 4 $\times$ (mm) = 4 mm

Circular scale reading is 60 $\times$ 0.01 = 0.6 mm

Observed reading is $R_{0}$ = 4 + 0.6 = 4.6 mm

So True reading $R_{0} - e$ = 4.6 - 0.05 = 4.55 mm

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