Viva Voice Question
Spherometer – Viva Voice Questions with Answer
For: Science Class 11 ( Practical Exam )

Q.1: Why the instrument is given the name “spherometer”?
Ans. Because it is used to determine the radius of curvature of a spherical surface.

Q.2: What is the pitch of a spherometer?
Ans. The distance covered by the circular disc in one complete rotation along the main scale. Mostly pitch of spherometer = 1 mm = 0.1 cm.

Q.3: How do you find the least count of spherometer?
Ans. L.C. of spherometer = (Pitch of screw / No. of divisions an circular scale) = (0.1 cm / 100) = 0.001 cm.

Q.4: What is meant by ‘radius of curvature’ of a surface?
Ans. The radius of that sphere from which the surface is cut.

Q.5: What is the radius of curvature of phone surface?
Ans. Infinite.

Q.6: What is the formula for the radius of curvature?
Ans. R = (a^2/6h) + (h/2)
Where,
a = mean distance between the legs of the spherometer, and
h = height or depth of a surface

Q.7: Is there any zero error in a spherometer?
Ans. Spherometer may have a zero error. Z.E. in spherometer = reading on the plane glass sheet

Q.8: When the zero error (Z.E.) is positive and when negative?
Ans. Positive: If the edge of the circular disc is at zero of main scale and the zero of the circular scale is ahead of the edge of main scale. If it is behind the edge of main scale, the Z.E. is negative.

Q.9: Can you measure the radius of curvature of wrist-watch glass by using a spherometer?
Ans. No, because the wrist-watch glass is small and all the legs of the spherometer cannot rest on it.

Q.10: What will be the effect of:
(a) changing the pitch or
(b) changing the number of circular divisions upon accuracy or least count.
Ans. (a) If we decrease the pitch the L.C. will decrease and hence the accuracy increases.
(b) If we increase the No. of circular divisions, the accuracy increases since the L.C. decreases.

Q.11: What are the other uses of spherometer?
Ans. (a) In finding a small increase in length during finding the coefficient of linear expansion.
(b) In finding the small change in length due to the change in the weight suspended during the
determination of young’s modules.

Q.12: Why main scale is marked on both sides of zero?
Ans. To measure both height and depth.

Q.13: Is paper insertion method for testing the touching position of the screw is correct?
Ans. No, because the thickness of ordinary paper (0.01 cm) is greater than the L.C.

Q.14: Define focal length?
Ans. The distance between the pole and the principal focus of spherical mirror is called the focal length. The focal length of spherical mirror is half of its radius of curvature.