Learning physics and chemistry easily and freely - Science for elementary school, middle school and high school

Free online optic lesson for elementary school,  middle school and high school.


Propagation of light

Beams of light

1) What is a beam of light ?

Generally, a light source emits light in in several directions: All the rays of light then correspond to a light beam.

A beam of light can be represented by drawing its upper and lower ray of light.
Example: Beam of light from a flashlight

Beam of light from a flashlight

2) Can we see a beam of light ?

When a screen is lighted by a flashlight, we can see a spot of light on this screen because it diffuses (like other secondary sources) the received light. Nevertheless the beam of light between the flashlight and the screen can't be seen.
Light emitted by a ( primary or secondary ) source enables to see this source but light emitted can't be seen.

However, we can visualize a beam of light with particles (dust, smoke or even drop of water) that behave as diffusing objects when located within the beam of light

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