Laser Microscope

Aim: To find the average size of microbes in a water sample using laser microscope.

Apparatus: Water sample with microbe culture, syringe, laser source (wavelength = 635 nm), scale, retort stand, screen


A plastic syringe contains water sample with microbe culture. A water droplet is formed at the open end of the syringe when the piston of the syringe is gently pressed. A Laser beam is focused on the droplet. On the screen, we see a magnified image of the microbes present in the water droplet. Around the magnified image of the microbes, we observe a diffraction pattern. By studying this diffraction pattern, we will find their average size.

Schematic representation of the set-up

Fig.1 The photograph of the pattern obtained on the screen


  1. From the photographs given below, generate the relevant data from the diffraction patterns.
  2. Devise your procedure to generate the data with 1% uncertainty. Find the average size of microbes present in the water sample used here.



The average size of microbes present in the given water sample is _______________

%d bloggers like this: