Class 11 Physics practical reading To measure radius of curvature of a given spherical (convex) surface by a spherometer.

Aim

To measure radius of curvature of a given spherical (convex) surface by a spherometer.

Apparatus Required

A spherometer, a convex surface, a plane glass strip, a scale (15 cm) and a sharp pointed pencil.

Theory

A spherometer is a device based on the principle of micrometer screw. It can be used to measure the height of curved surface with an accuracy of 0.001 cm.

A Spherometer

Procedure

1. Raise the central screw of the spherometer and press the spherometer gently on the white side of practical note book. Mark the points as A, B and C.
2. Measure the distance between points by joining them to form a triangle A B C, i.e., AB, BC and AC.
3. Determine the pitch and least count of the spherometer and record it.
4. Raise the screw and place it on convex surface.
5. Turn the screw downwards till the screw tip just touches the convex surface.
6. Note the reading of the circular scale which is in line with the vertical scale (take it as reference).
7. Remove the spherometer and place over a large size plane glass slab. Repeat steps 5 and 6 two more times and record observations in tabular form.

Observations

Precautions

1. The screw should move freely without friction.
2. The screw should be moved in the same direction so as to avoid backlash error.
3. Excess rotations should be avoided. 4. Central screw should just touch the curved (or plane) surface.

Sources of Error

1. The screw may have friction.
2. The screw may be loose.
3. The spherometer may have backlash error.