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Assuming the light is emitted uniformly in all
directions, at what distance from the lamp will
the rate of green photons flowing outward (the
“intensity”) be 106 photons.cm-2
.s-1 (i.e. 1
million photons per square cm per second)?
This is approximately the apparent brightness
of a bright star.

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Elin Hessel
Elin HesselLv2
1 Apr 2019

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Related textbook solutions

Physics: Principles with Applications
7th Edition, 2013
Giancoli
ISBN: 9780321625922

Related questions

7. (a) If the average frequency emitted by 200 W light bulb is 5.00E14 Hz and 10.0% of the input power is emitted as visible light, approx how many visible light photons are emitted per second? (b) At what distance would this correspond to 1.00E11 visible light photons per square centimetre per second if the light is emitted uniformly in all directions?

The “resolving power” of any optical system is limited by thewave-like property of light–and photons–through diffraction orinterference. This is often described by the “Rayleigh criterion”which states that the minimum angular separation dR for two objectsto be resolved by an optical system having a circular aperture ofdiameter D using light of wavelength ? is dR = 1.22 ?/D. What isthe minimum distance d between two points on the earth’s surfacecan be resolved by the GeoEye optical system discussed in theprevious question at anominal wavelength of ? = 550 nm?

(Refer this question as Previous question)
Often, sodium vapor lamps are used to illuminate large outdoorareas because they
mainly radiate at two nearly equal wavelengths, the sodium yellow“D” lines ? =589 nm. Suppose a 1 kW lamp is 50% efficient atproducing photons at this wave-length. How many such photons areproduced per second? Assuming the photons radiate isotropicallyfrom the lamb, how may photons enter the pupil of one of your eyesif you are standing 100 m from the lamp? Assume the pupil to have aradius of 1 mm.
Now suppose the“GeoEye-1” satellite, a supplier of images forGoogle-Earth, is
observing the area around the lamp at night. Assume the satellitecollects all the
photons hitting a 1 m diameter circular aperture formed by itsimaging system when
it is looking straight down from its orbital altitude of 681 km.How many photons
per second are collected from the lamp by GeoEye?

**Explain in details please**

 

Solar Sail
A solar sail allows a spacecraft to use radiation pressure for propulsion, similar to the way wind propels a sailboat. The sails of such spacecraft are made out of enormous reflecting panels. The area of the panels is maximized to catch the largest number of incident photons, thus maximizing the momentum transfer from the incident radiation.
For such spacecraft to work, the force from the radiation pressure exerted by the photons must be greater than the gravitational attraction to the star emitting the photons. The critical parameter is the area density (mass per unit area) of the sail.
Part A
  
Consider a perfectly reflecting mirror oriented so that solar radiation of intensity is incident upon, and perpendicular to, the reflective surface of the mirror. If the mirror has a surface area, what is the magnitude of the average force due to the radiation pressure of the sunlight on the mirror?
Express your answer in terms of the intensity, the mirror's surface area, and the speed of light.
ANSWER:
 
=
(2IA)/c
Correct
   
To solve the second part of this problem you will need to know the following:
  • the mass of the sun, M sun= 2.0 x 1030 kg,
  • the intensity of sunlight as a function of the distance from the sun,
Isun(R) = 3.2 x10251/R2 (W/m2)
and
  • the gravitational constant G=6.67 x10-11m3/(kg*s2)
Part B
  
Suppose that the mirror described in Part A is initiallyatrest a distance away from the sun. What is the critical valueofarea density for the mirror at which the radiation pressureexactlycancels out the gravitational attraction from the sun?
Express your answer numerically, to twosignificantfigures, in units of kilograms per metersquared.
ANSWER:
 
mass/area =
Answer not displayed
    
I'm having trouble figuring out how to slovepart B.Thanks!

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