0
Closed
Force due to light from a point source
A point source of light emits isotropically with a power of 200 W. What is the force due to the light on a totally absorbing sphere of radius 2.0 cm at a distance of 20 m from the source?
Customer support service by UserEcho
I'm not sure what part you are stuck on, so I will try to give you tips throughout.
Use the power and distance to find the flux/time/area at 20 m away
Because the sphere is small compared to the distance, approximate it to be a circle facing the source
Find the flux on the circle using the flux/area you found
Now is where you have to think. The units of what you have are Energy/time. force is dp/dt.
You have Energy transferred to the sphere per time and you want momentum transfer per time.
Knowing this is light, can you get the momentum from known energy?
Hope this helps!