Question

What do you mean by dynamic spherometer?

Answer 1

Let us first get some idea about the spherometer. A spherometer is a device that measures the radius of curvature of a sphere or curved surface with great accuracy. Originally, opticians utilised these instruments to measure the curvature of a lens' surface curvature.

Complete step-by-step solution:
Let's get some more ideas about it. The usual form consists of a fine screw moving in a nut carried on the center of a $3$ small legged table or frame; the feet forming the vertices of a triangle. The lower end of the screw and those of the table legs are finely tapered and terminate in hemispheres, so that each rests on a point. If the screw has two turns of the thread to the millimetre the head is usually divided into $50$ equal parts, so that differences of $0.01$millimeter may be measured without using a vernier. A lens, however, may be fitted, in order to magnify the scale divisions. A vertical scale fastened to the table indicates the number of whole turns of the screw and serves as an index for reading the divisions on the head.
Basically if we can say that a spherometer is a device that measures the radius of a sphere's curvature. A more accurate gadget for the same is a dynamic spherometer.

Note: The spherometer can be used for reasons other than measuring the curvature of a spherical surface because it is essentially a form of micrometre. It can, for example, be used to determine the thickness of a thin plate.
To do so, position the instrument on a perfectly level plane surface and turn the screw until the tip just contacts; the precise moment when it does so is marked by a quick decrease in resistance followed by a significant increase. The screw is elevated, the thin plate is put under it, and the operation is repeated. The needed thickness is determined by the difference between the two readings.