The Vernier Scale
The Vernier Scale is a very useful scale to use as it allows the measurement of a length or distance to be measured as accurately as ±0.01mm. The scale is used extensively within the Waves sub-unit, when measuring fringe separation in interference patterns for example.
The video below shows a guide to reading a Vernier Scale:-
Below is some example Vernier Scales (each division = 0.1mm), with the correct measurements shown:-
Vernier Calipers
Vernier Calipers comprise a calibrated scale with a fixed jaw, and another jaw, with a pointer, that slides along the scale. The distance between the jaws is then read using the Vernier scale.
Below is some example Vernier Calipers (each scale division = 0.02mm), with the correct measurements shown:-
Micrometer
The Micrometer is another device that can be used to make very accurate measurements of a length or distance. Micrometers use a screw to transform small distances (that are too small to measure directly) into large rotations of the screw that are big enough to read from a scale.
The video below shows a guide to reading a Micrometer:-
Below is some example Micrometers (each scale division = 0.01mm), with the correct measurements shown:-
Spherometer
The Spherometer is a device that is used to make very accurate measurements of a curved surface. Spherometers use the difference in poistion between a set of four points to allow the curvature of an object, such as a lens, to be measured.
The video below shows a guide to reading a Spherometer :-
To find the radius of curvature of an object, follow the procedure below :-
Firstly, using vernier calipers, measure the lengths between them as shown, then find an average value of the length (l) and state the value in mm :-
FInd the 'pitch' pf the spherometer by finding how far on the vertical scale (P) is moved through in one complete revoloution of the disc. Then find the 'least count' (l.c) of the spherometer by using the following equation :-
To check for a systematic error in the zero position, place the spherometer on a flat glass sheet, bring the central pin into contact and read the value on the disc. If this is non-zero, then the value of the offest can be calulated by :-
The height difference (h) in mm between the 'legs' and the 'central pin' can be calculated by :-
Note - It is at this point that any 'zero error' can be removed from the measurement by subtraction.
The 'Radius of Curvature' of the object (in mm) can then be calculated by :-
