PHYSICS LAB MANUALS

Newton's rings

  1. Switch on the sodium vapour lamp.

  2. Adjust the reflector glass plate at 45° so that the light now travels towards the table top vertically downwards.

  3. Illuminate the Newton ring set up (Plano-convex lens and the glass plate) with this light.

  4. Look down vertically from above through a travelling microscope. Make adjustments to clearly see a bright spot with rings around it. To achieve this, adjust microscope.

  5. Once good rings are in focus, rotate the eyepiece such that out of the two- perpendicular cross-wires, one has its length parallel to the direction of travel of the microscope. Let this cross-wire also pass through the center of the ring system.

  6. Now move the microscope to focus on a ring (say, the 20th order bright ring), on one side of the center. Set the crosswire tangential to the microscope reading.

  7. Move the microscope to make the crosswire tangential to the next ring nearer to the center and note the reading. Continue with this process till you pass through the center and to the other end.

  8. Repeat this process after putting 1-2 drops of water between the lens and the glass-plate in order to produce a thin film of water.

Make the following table –

Table II : The details of the physical quantities to be measured.

S.No

Physical quantity

Independent /

Dependent

Measured

with

Measuring instrument’s

Minimum

Maximum

Least count

1

Length

Independent

Travelling microscope

0.5mm

100mm

0.01mm