PHYSICS LAB MANUALS

SINGLE SLIT DIFFRACTION

Three physical quantities need to be measured in this experiment – Slit width (\(d\)), Distance between slit and screen (\(D\)) and Displacement (or position of maxima) on screen (\(x\)). 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

Slit width (\(d\))

Independent

Micrometer

0.01 mm 0.01 mm

2

Distance between slit and screen (\(D\))

Independent

Meter scale

1 mm 1000 mm 1 mm

3

Displacement (or position of maxima) on screen (\(x\))

Independent

Vernier scale

0.1 mm 0.1 mm

A. Intensity vs displacement on screen:-

  1. Level the optical rail with the table.

  2. Set up the laser diode and slit on the optical rail in proper alignment.

  3. Fix the distance at which the screen should be from the slit.

  4. Adjust slit width (and measure it using micrometer) and observe on the screen for a distinguishable diffraction pattern.

  5. Set the photodetector at optimum height and check for highest intensity at central maximum.

  6. Take intensity reading on detector as a function of displacement (measured using Vernier scale) on both sides.

B. Wavelength of light:-

  1. Keeping the setup undisturbed, replace the photodetector with a screen.

  2. Using the Vernier scale attached with screen, mark the positions of maxima till 5-7 orders on either side.

  3. By calculating fringe width of different orders from the difference in positions of maxima, find the wavelength of light by taking average.