Radiation pressure of a light bulb

AI Thread Summary
The discussion focuses on estimating the radiation pressure from a 100 W light bulb at a distance of 8.4 cm. Relevant equations include the relationship between power, force, and pressure, specifically using the Poynting vector and the speed of light. The user calculates the cross-sectional area and attempts to derive force from power and distance but encounters a challenge due to the absence of time in the given data. They deduce that force can be expressed as power divided by the speed of light, leading to the conclusion that pressure equals intensity divided by the speed of light. It is noted that this calculation assumes the light is absorbed, as reflected light would result in double the pressure.
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1. Homework Statement
Estimate the radiation pressure due to a 100 W bulb at a distance of 8.4 cm from the center of the bulb.

2. Relevant equations
Power= Work/Time W=Force(distance)

Pressure = Force/Area = Poynting vector/speed of light

3. The Attempt at a Solution
I found the cross sectional area by doing 4∏ r^2, so I have that. Then, seeing as I was given power and distance, I tried to figure out the Force in terms of Power and distance, but in doing that, I got the formula F= Power (Time)/distance, and I wasn't given the time. Is there some formula that I'm missing?
 
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distance/Time is velocity ... so your "(Time)/distance" = 1/c .
This means that your F= Power/c ... Pressure = Intensity/c .

Note that this is only true if the 100W of light is absorbed
(light being reflected would double the pressure)
 
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