PHYSICS LAB MANUALS

Reflectance and Transmission

Three physical quantities need to be measured in this experiment – angle of incidence and amount of reflected and transmitted light. Make the following table –
Table II: The details of the physical quantities to be measured.

S. No

Physical quantity

Dependent or Independent

Measured with

Measuring instrument’s

Minimum

Maximum

Least count

1

Angle of incidence

independent

Spectrometer

 0° 360° 0.5°

2

Intensity of the reflected beam

Dependent

Photodetector

 0µA mA 0.1µA/mA

3

Intensity of transmitted beam

Dependent

Photodetector

 0µA mA 0.1µA/mA

  1. Switch on the laser . Wait for couple of seconds to see the light coming out of the laser.

  2. Align the laser ligth in a straight line – parallel to the plane of the table and also to one of the edges of the table.

  3. Take the spectrometer table with sample mounted on it. Adjust it such that laser light passes exactly over the axis of its rotation. Also make adjustment to see that the reflected light at 0O angle of incidence falls on the opening of the laser.

  4. Rotate the spectrometer table and check if the reflected beam is same plane for all the angle of incidence.

  5. Fix the angle of incidence for which the reflected light is minimum. Now place a polarizer between source and glass plate and adjust its angle such that intensity of reflected beam is minimum.

  6. Keeping the angle of polarizer fixed in this position, note down the reflected and transmitted light by changing the angle of incidence in steps of 5O. Use two photodiodes for this purpose.

  7. Change the angle of incidence in steps of 1O , where the reflected light sees a minimum.

  8. Change the angle of polarization by 90° and repeat step 6 and 7. This corresponds to \(\perp\) polarization of light.