To Learn the Parts of a Travelling Microscope and to read a reading

Aim of the Experiment

To learn the parts of a Travelling Microscope and to read a reading.

Apparatus Required

Reading lens and capillary tube.

Design of the Instrument

Travelling Microscope consists of an ordinary compound microscope which slides along a graduated vertical pillar, attached to horizontal base resting on the leveling screws. The main scales divisions along with vernier scale divisions are marked on the horizontal base and the vertical pillar.

The microscope can be moved up and down in the vertical pillar and can be moved in to and fro direction over the horizontal base. Thus the microscope can be moved both in the vertical and horizontal directions. Two fine adjustment screws are provided for the horizontal and vertical movements respectively.

The image of the object can be focused by adjusting the side screw (S) attached to the microscope. The eye piece of the microscope is provided with a cross wire.

Experiment Theory

It is a compound microscope attached to a graduated vertical pillar, which is mounted on rigid platform as shown in the figure below. The platform is provided with three leveling screws. The microscope can be set with its axis either in the vertical or the horizontal position. The microscope can be moved in the vertical or horizontal direction by means of a screw arrangement attached to it. The distance through which the microscope is moved is read on the scale. There are two scales one for horizontal movement and the other for the vertical movement.

Each scale has a main scale (M1, M2) and a vernier scale (V1, V2). The vernier moves with the microscope. As in the spectrometer, there is a set of main screw and fine adjustment screw, for the horizontal and the vertical movements. One set is fixed to the pillar for vertical movement and the other set is fixed to the platform for horizontal movement. The eyepiece of the microscope is provided with cross-wires. The image of an object is focussed by the microscope using a side screw (focusing screw) attached to the microscope.

Procedure

1. To find the Least Count (LC) of the travelling microscope:

The main scale is graduated in mm. There are 50 V.S.D equivalent to 49 M.S.D. The value of one M.S.D. is 0.5 mm = 0.05 cm

• LC = 1 M.S.D - 1 V.S.D.
• 1 M.S.D = 0.05 cm
• 50 V.S.D = 49 M.S.D
  
• 1 V.S.D = 49/50 x 0.05 = 0.049 cm
  
• LC = 0.05 - 0.049 cm
  
• LC = 0.001 cm

2. To read a reading:

When the microscope is clamped by the main screw or fine adjustment screw at any position, the reading is taken in the vertical scale or in the horizontal scale according to the requirement. M.S.R and V.S.R are taken as in the vernier calipers. For example see below figure and write the M.S.R and V.S.R

Note: In the Vernier calipers, travelling microscope and the spectrometer, the MS zero may coincide with the VS zero. In such cases, the MSD, which coincides with the VS zero is the MSR reading.

Observation

Least Count L.C = 0.001 cm

Result

The parts and functions of the travelling microscope are studied and a few readings are taken.

Viva Questions and Answers

Question: Why travelling microscope is called so?
Answer: Travelling microscope is called so because it can be moved in horizontal and vertical directions to take measurements while seeing the magnified image of the object under study. It can be used to determine the diameter of capillary tube, to determine the refractive index of the material of a glass slab by measuring real depth and apparent depth etc.

Question: What type of eye-piece is used in a travelling microscope?
Answer: Ramsden’s eye piece

Question: What is role of lycopodium powder on the upper surface of glass slab while determine refractive index by travelling microscope?
Answer: So that we can focus over the surface of glass slab.

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