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Radiation Pressure

  1. Dec 4, 2016 #1
    1. The problem statement, all variables and given/known data
    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.)

    2. Relevant equations

    3. 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)
  2. jcsd
  3. Dec 4, 2016 #2
    Would the equation be:

    Prad = I / c ?

    Plugging stuff in, this is what I get:

    c = 1/√(μoεo)
    I = P/ (SA)
    Prad = 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
  4. Dec 4, 2016 #3


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    I would assume the absorbing case here. Please quote it.
  5. Dec 4, 2016 #4


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    Looks right, except your fingertip will have some reflectivity.
  6. Dec 4, 2016 #5
    Great thanks!
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