Wednesday, November 17, 2010

Physics Practical:: Measurement of diameter of capillary tube using travelling microscope.

Shalini asked:

How to do calculation in the physics practical(capillary rise method) to measure the diameter of the capillary tube?

A Travelling Microscope

image A travelling microscope is used to determine small distance to an accuracy of 0.001 cm. The measurement principle is based on the principle of vernier. In a typical travelling microscope, the main scale divisions are of magnitude 0.05 cm (0.5 mm) each and the vernier scale contains 50 divisions. This makes the Least Count to be 0.05/50 = 0.001 cm.

Determination of diameter

For determination of diameter of the capillary along the horizontal direction

Mount the capillary tube in horizontal direction in a stand with the help of a rubber cork to place and hold the capillary tube. Rotate the microscope so that it is horizontal and in line with the tip of the capillary tube.

imageNow looking through the microscope, turn the focussing screw to get a clear image of the capillary tube. Now adjust the microscope in such a way that the vertical crosswire coincides with the left end of the capillary tube.

Take the reading

In the horizontal scale, look the zero of the veriner, and find out the division on the main scale just before the zero mark. Note it as the MSR.

Now look carefully at the vernier. Any one of the fifty lines will come exactly in line with one of the lines of the main scale. That division on the vernier  is the vernier scale reading. note it down in the observation table.

Now move the telescope horizontally to focus on the right end of the capillary tube. Again take the reading as before.


Repeat the experiment by moving the telescope vertically coinciding the horizontal crosswire with top and bottom and now the readings are taken on the vertical scale.

From the observations you will get two values of diameter, one for vertical and one for the horizontal.


Least count of the traveling microscope = …… cm


1 comment:

  1. truely useful to me. for my homeworks =)


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