Welcome to practical physicsPracticle physics - practical activities designed for use in the classroom with 11 to 19 year olds
 

Fine cloth as a grating

Class Practical

Observing a two-dimensional diffraction pattern.

Apparatus and materials

Light source, compact

Retort stand, boss, and clamp

Power supply, low voltage, variable, to supply 8A at 12V

Woven cloth, many pieces

Health & Safety and Technical notes


Read our standard health & safety guidance

Use a compact light source, rather than a line filament lamp, since this is a two-dimensional grating.  

The cloth should be of a simple square weave with holes between the threads to let the light through. The samples should be large enough for students to hold with two hands and try stretching and shearing. Old umbrella cloth works well. 

 

Procedure


Each student looks towards the lamp and holds a piece of cloth in front of one eye. Ask them to observe the pattern as they try stretching and shearing the fabric.


Teaching notes


The cloth acts like crossed gratings. Indeed, as preparation, it might help to show two gratings, initially in line, and then rotate one. 

Encourage students to be observant outside the lab. Looking at sodium street lamps through domestic net curtains is very effective, especially if there are lamps at various distances. 
 
This experiment was safety-checked in February 2006

 

Related experiements


Coarse diffraction grating