Page 30 - Physics - XI

Observations

Value of the smallest division on the vertical Pitch scale = _________ mm
Number of complete rotations of the circular disc = a = _________
Distance moved by screw for a rotations of the circular disc = b = _________ mm

b
Pitch of the Screw = = _________ mm
a
Total number of divisions on the circular scale = N = _________

Least count = Pitch of the Screw = _________ mm
N
Distance between the two legs of the spherometer (Fig. 4.2)

(i) AB = _________ cm (ii) BC = _________ cm (iii) CA = _________ cm

Mean distance (l) between the two legs

l = AB + BC + CA = _________ mm
3
Table for calculation of Sagitta (h)

S. Reading of the Reading on the plane glass plate Fractional rotation = h = n × pitch + m × L.C.
No. circular scale on m = diff erence between (mm)
the convex surface No. of complete Circular scale x and y
rotations reading m = x – y
x n y
1.
2.

3.
4.

Mean (h) = h + h + h + h 4 = ______ mm = ______ cm
2
1
3
4
Calculations
Substitute the value of h and l in the formula

R = l 2 + h
6 h 2
= ______ cm

Result

The radius of curvature of the given spherical surface is _________ cm.

Precautions
1. The screw should always be rotated in the same direction to avoid backlash error.

2. The screw should move freely without friction.
3. The readings of the circular scale should be taken carefully just to touch position of the screw tip.

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