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Q & A: light and force

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Most recent answer: 05/10/2018
Q:
When turning a flashlight on is any force exerted the opposite way of the light?
- Matthew Kellogg (age 15)
Murrieta,California,USA
A:

Yes, but it's very weak. Say that a 1 watt beam of light goes forward from the flashlight. The backward force on he light is 1W/c, where c is the speed of light, 3*108 m/s, So that force is 3.3*10-9 Newtons. For comparison, the weight of the flashlight is probably more than 1 N.

Mike W.


(published on 05/10/2018)

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