How Much Thrust Does a 1W Flashlight Emit?

  • Thread starter Thread starter jacobgong
  • Start date Start date
  • Tags Tags
    Thrust
AI Thread Summary
A 1W flashlight emits thrust due to the momentum of light, which can be calculated using the equation for light's momentum. The force exerted by the flashlight is related to the wavelength of the emitted light, with 500nm light being specified in the discussion. When a perfect mirror is placed in front of the flashlight, it would receive the same amount of force due to the conservation of momentum, as light reflects off the mirror. Participants emphasize the importance of showing effort in calculations to facilitate learning. The thrust produced by such a flashlight is expected to be extremely small and negligible in practical applications.
jacobgong
Messages
4
Reaction score
0
What would be the thrust from a 1W light output flashlight, assuming light is not scatered at all.
I'm not sure but if it depends on the wavelength, assume it only emits 500nm light.

and if I were to put a perfect mirror right infront of this flashlight would the mirror receive the same amount of force?
please breifely explain how it's calculated. (the equation and the Plank's constant?)
 
Physics news on Phys.org
Well, light has momentum, so you can just use the standard conservation laws and the equation for light's momentum to calculate any "thrust", or reaction force, you wish. As far as mirrors are concerned, remember momentum is a vector.
 
jacobgong said:
What would be the thrust from a 1W light output flashlight, assuming light is not scatered at all.
I'm not sure but if it depends on the wavelength, assume it only emits 500nm light.

and if I were to put a perfect mirror right infront of this flashlight would the mirror receive the same amount of force?
please breifely explain how it's calculated. (the equation and the Plank's constant?)

Welcome to the PF, Jacob. Per the PF Rules link at the top of the page, we shouldn't offer you help until you post the relevant equations and show some work/effort on your part. That's how we try to help you learn how to learn, eh?
 
well I can garentee you I'll never be asking about any homeworks. I only ask for personal interest. That's the reason for my simple numbers, because it's just a question i randomly made up.
it's not like I'm trying to make anyone to work for me or anything like that.

so you see if I didn't even try, and you tell me the answer, i don't benifit at all. and I know the answer is going to be so small it won't make any sense in this application.
 
Kindly see the attached pdf. My attempt to solve it, is in it. I'm wondering if my solution is right. My idea is this: At any point of time, the ball may be assumed to be at an incline which is at an angle of θ(kindly see both the pics in the pdf file). The value of θ will continuously change and so will the value of friction. I'm not able to figure out, why my solution is wrong, if it is wrong .
TL;DR Summary: I came across this question from a Sri Lankan A-level textbook. Question - An ice cube with a length of 10 cm is immersed in water at 0 °C. An observer observes the ice cube from the water, and it seems to be 7.75 cm long. If the refractive index of water is 4/3, find the height of the ice cube immersed in the water. I could not understand how the apparent height of the ice cube in the water depends on the height of the ice cube immersed in the water. Does anyone have an...

Similar threads

Back
Top