Show that the radiation pressure that a plane EM wave exerts on a surface, a perpendicular incidence, is equal to the energy density of the field for a perfectl absorbing surface, and twice that for a perfectly reflecting surface. Find expressions for the radiation pressure in (a) for the case of non-perpendicula incidence. One of the reasons comet tails form and always point away from the Sun is th radiation pressure force. Assuming the average power output x1026 Watt, estimate the radiation pressure force on a small 20 kg "dust" materia of area 0.2 m² of a comet orbiting at a distance 5 x 1010m from the the Sun Comment on whether this force would be enough to move the dust away from th orbit of the comet. the Sun to be
Show that the radiation pressure that a plane EM wave exerts on a surface, a perpendicular incidence, is equal to the energy density of the field for a perfectl absorbing surface, and twice that for a perfectly reflecting surface. Find expressions for the radiation pressure in (a) for the case of non-perpendicula incidence. One of the reasons comet tails form and always point away from the Sun is th radiation pressure force. Assuming the average power output x1026 Watt, estimate the radiation pressure force on a small 20 kg "dust" materia of area 0.2 m² of a comet orbiting at a distance 5 x 1010m from the the Sun Comment on whether this force would be enough to move the dust away from th orbit of the comet. the Sun to be
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Transcribed Image Text:Show that the radiation pressure that a plane EM wave exerts on a surface, at
perpendicular incidence, is equal to the energy density of the field for a perfectly
absorbing surface, and twice that for a perfectly reflecting surface.
Find expressions for the radiation pressure in (a) for the case of non-perpendicular
incidence.
One of the reasons comet tails form and always point away from the Sun is the
radiation pressure force. Assuming the average power output of the Sun to be 4
x1026 Watt, estimate the radiation pressure force on a small 20 kg "dust" material
of area 0.2 m² of a comet orbiting at a distance 5 x 1010m from the the Sun.
Comment on whether this force would be enough to move the dust away from the
orbit of the comet.
Transcribed Image Text:Voyager 2.
When the Voyager 2 spacecraft was approaching towards its Neptune encounter in
1989, it was 4.5 × 10° km away from the earth. Its radio transmitter, with which it
communicated with us (and we communicated with it), broadcast with a mere 22 Watt
of power at the S-band (2.1 GHz). (Your home wi-fi router emits around 2 Watt at 2.4
GHz wi-fi band). Assuming the Voyager transmitter broadcast equally in all directions,
(a) What signal intensity was received on the earth?
(b) What electric and magnetic field amplitudes were detected?
(c) How many 2.1 GHz photons were arriving per second on a radio-receiver antenna
with a circular cross-section of diameter 34 meters?
Two counter-propagating plane waves
(a) Let E(z, t) = E0 cos(kz – wt)â + E, cos(kz + wt)x. Write E(z, t) in simpler form
and find the associated magnetic field.
(b) For the fields in part (a), find the instantaneous and time-averaged electric and
magnetic field energy densities.
(c) Let E(z, t) = E, cos(kz – wt)x + E, sin(kz + wt)ŷ. Determine the polarization of
the field at z = 0, z = X/8, z = \/4, z =
31/8, and z =
= /2.
(d) Find the time-averaged Poynting vector as a function of z for the field in part (c).
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