4. Measure the diameter of a given wire using screw gauge.

Aim:- To measure diameter of a given wire using screw gauge.

Apparatus:- Screw gauge, wire, half-meter scale and magnifying lens.

Theory:- 

   If with the wire between plane faces A and B, the edge of cap lies ahead of n^th division of linear scale.

Then, linear scale reading (L.S.R)   =   N

   If n^th division of circular scale lies over reference line.

Then, circular scale reading (C.S.R) = n x (L.C) [L.C is least count of screw gauge]

Total reading (T.R) = L.S.R + C.S.R = N + n x (L.C)

If D be the mean diameter and l be the mean length of the wire,

            Volume of the wire, V = π (D/2)² l

Observation:-

Determination of Least count of the Screw Gauge

                       1 L.S.D = 1mm.

Number of full rotations given to screw = 4mm

Distance moved by the screw = 4mm

Hench, pitch, P = 4mm / 4 = 1mm.

No. of division on circular scale = 100

Hench, least count = 1mm / 100 = 0.01mm = 0.001 cm

Zero error = 0mm

Mean zero error (e) = 0mm

Mean Zero correction (c) = -e = 0mm

Table for Diameter:

Serial Number	Main Scale Reading	Circular Scale Reading		Total Reading
		No. of circular scale division on reference line(n)	Value[n x (V.C)]	Observed [Do = N + n x (V.C)]	Corrected )D = Do + C)
1					D1
2					D2
3					D3
4					D4
5					D5
6					D6

Screw gauge measuring diameter of the wire

Table for length:

Serial Number	Main Scale Reading	Vernier Scale Reading		Total Reading
		No. of Vernier division coinciding	Value [n x (V.C)]	Observed [Lo = N + n x (V.C)]	Corrected (L = Lo + C)
1					L1
2					L2
3					L3

Calculations:-

Mean Diameter of the wire, D = D₁ + D₂ + D₃ + D₄ + D₅ + D₆ / 6

Mean Length of wire = L₁ + L₂ + L₃ / 3

Volume of the wire, V = π (D/2)² l

Result:-

The volume of the given wire is ………. cm³

Precautions:-

1. To avoid undue pressure; the screw should always be rotated by ratchet R and not by cap K.
2. The screw should move freely without friction.
3. The zero correction, with proper sign should be noted very carefully and added algebraically.

Sources of Error:-

1. The screw may have friction
2. The screw gauge may have back – lash error.
3.  Circular Scale divisions may not be of equal size.