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29. (a) The upward force supplied by radiation pressure in this case (Eq. 3332) must be
equal to the magnitude of the pull of gravity (
mg
).
For a sphere, the “projected” area
(which is a factor in Eq. 3332) is that of a circle
A
=
π
r
2
(not the entire surface area of
the sphere) and the volume (needed because the mass is given by the density multiplied
by the volume:
m
=
ρ
V
) is
3
4/
3
Vr
π
=
.
Finally, the intensity is related to the power
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This note was uploaded on 06/03/2011 for the course PHY 2049 taught by Professor Any during the Spring '08 term at University of Florida.
 Spring '08
 Any
 Physics, Force, Gravity, Radiation

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