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Welcome to our Physics lesson on Pressure of Light, this is the third lesson of our suite of physics lessons covering the topic of The Compton Effect and Pressure of Light, you can find links to the other lessons within this tutorial and access additional physics learning resources below this lesson.
The interaction between light and matter is manifested in many ways such as through reflection, refraction, photoelectric effect, scattering etc. Among them there is the pressure effect of light as well (pressure exerted by light on the surface of objects).
The values of light pressure are very small; they vary between 10-6 Pa - 10-8 Pa. The phenomenon of light pressure was initially observed by Pyotr Lebedev at the early 1900s. He found that light pressure depends on the following factors:
Combining these factors, Lebedev found the following formula for light pressure P:
We know that 0 ≤ r ≤ 1 where r = 0 for black bodies and r = 1 for perfect mirrors. Therefore, light pressure in perfect mirrors is twice the pressure produced by the same light beam on black bodies for the same incident angle.
In astronomic dimensions, the effect of light pressure is clearly observed in comets. When a comet approaches the Sun, its gaseous tail elongates and moves away from the Sun. This phenomenon occurs due to the high pressure of light emitted from the Sun.
Pressure produced by powerful lasers can reach values up to tens of atmospheres (millions of Pascals) as it is a beam with a concentrated energy on small surfaces. This is why laser beams are used in surgery and technology to cut things with high precision.
You have reached the end of Physics lesson 19.3.3 Pressure of Light. There are 5 lessons in this physics tutorial covering The Compton Effect and Pressure of Light, you can access all the lessons from this tutorial below.
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