Estimate the radiation pressure

[ooohffff]

Homework Statement

a) Estimate the radiation pressure due to a 100 W bulb at a distance of .08 m from the center of the bulb.
b) Estimate the force exerted on your fingertip if you place it at this point. (Assume an area of .0001 m² for the fingertip.)

Homework Equations

F=P_radA

The Attempt at a Solution

a) I'm assuming the radiation is like a sphere. I'm a little confused on what radiation pressure formula to use in this situation. I have formulas for perfectly absorbing and perfectly reflecting?

Power = 100W
r = .08m
SA = 4πr²

b) I know that the Force = Pressure * Area of fingertip, so I would need to get a) right to get b)

 

[ooohffff]

Would the equation be:

P_rad = I / c ?

Plugging stuff in, this is what I get:

c = 1/√(μ_oε_o)
I = P/ (SA)
P_rad = P / ( (SA)*c ) = 100W/ (4π(.08)²*c) = 4.15*10^-6 Pa

F= (4.15*10^-6 Pa) * (.0001 m²) = 4.15*10^-10 N

 

[haruspex]

I have formulas for perfectly absorbing and perfectly reflecting?

I would assume the absorbing case here. Please quote it.

 

[haruspex]

Would the equation be:

P_rad = I / c ?

Plugging stuff in, this is what I get:

c = 1/√(μ_oε_o)
I = P/ (SA)
P_rad = P / ( (SA)*c ) = 100W/ (4π(.08)²*c) = 4.15*10^-6 Pa

F= (4.15*10^-6 Pa) * (.0001 m²) = 4.15*10^-10 N

Looks right, except your fingertip will have some reflectivity.

 

[ooohffff]

Looks right, except your fingertip will have some reflectivity.

Great thanks!