How to measure the thickness of a given sheet using spherometer

Experiment : To measure the thickness of a given sheet using spherometer

Apparatus : Spherometer , Sheet (a metal sheet or a glass sheet) , a glass slab

How to Perform :

(i) Calculate the pitch and least count of a spherometer

(ii) Keep the given sheet on the glass slab

(iii) Turn the screw in anticlockwise direction to raise the central screw , so that given sheet could be kept under it and place the glass sheet under it . Adjust the central screw such that its tip just touches the sheet . (The tip of the screw would just touch its image in the glass sheet )

(iv) move the glass sheet

(v) Lower down the screw by the time its tip just touches the surface of the glass slab .

(vi) At the time of lowering down the screw , count the number of complete rotations made by the circular scale .

(vii) Repeat the experiment three times at various locations and record the observations .

Observations :

(i) Graduation of vertical scale = ……mm

(ii) Number of complete rotations given to the circular scale = a

(iii) Distance moved by screw in rotations (vertical scale) = b mm

$\displaystyle Pitch = \frac{b}{a} = …mm $

(iv) Total number of divisions on circular scale = N = …..

(v) $\displaystyle Least \; count = \frac{Pitch}{N} = … $

Calculations :

Mean value of the thickness of sheet $\displaystyle t = \frac{t_1 + t_2 + t_3}{N} = ….mm $

Outcome : The thickness of the given sheet is …


(i) Escape backlash error

(ii) The screw should move freely without friction.

(iii) The size of given sheet should be smaller than the glass slab .

Sources of Error :

(i) The pitch may not be constant at various locations of the screw does not have consistent threading .

(ii) Friction in the screw

(iii) The sheet may not be of consistent thickness

(iv) Backlash error

(v) Improper circular scale division