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Ray of light


A ray of light is a straight line used to describe the path of light as it travels through a medium. The ray is used to understand the behavior of light as it travels, refracts, reflects, and interacts with objects and surfaces.

The ray of light is used to discuss the phenomenon of light in a physics classroom. However, a students never see the light ray. Following demonstrations can be used to show ray of light:

Laser and incense stick

Take a plastic box with a lid. Open the lid and put some smoke in the box using an incense stick. Close the lid. Keep a laser torch just outside the box. Send laser light into the box from one side. You see the light beam very clearly. This also shows that light travels in a straight line.

Laser and chalk dust

You can sprinkle the chalk dust from the duster used on blackboard. The laser beam is clearly visible.

Laser and colloidal solution

Place a glass of tap water in front of a paper screen or wall. Shine a laser pointer (or a powerful torch) through the water. You will only see spots of light on the screen and on the wall of the glass. Now, put a drop of milk in the water and shine light through the water. You will be able to see the path of the light through the water.

What is the role of smoke or dust? How does it makes the laser light visible? The smoke or dust particles scatter the laser light towards our eyes and hence make it visible.


  1. Light Box
  2. Scattering of Light
  3. Experiments

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