A light sail is a propulsion technique that uses large sails to catch light and
ID: 1644764 • Letter: A
Question
A light sail is a propulsion technique that uses large sails to catch light and propel a vehicle in the vacuum of space. In a particular application, an Earth based laser illuminators such a sail perpendicularly with a beam of light of frequency 680 THz while emitting 3.9 times 10^41 photos per second. If 80% of the emitted photons reach the sail and are absorbed by it, find the resulting force in newtons, on a sail that is momentarily at rest with respect to the laser. Now assume the photons are reflected by the sail Keeping all the other assumptions of part (a), find the force the light beam exerts on the sail, in newtons. Ideally it would be best to me photons provided by natural sources to push the sail. If a star emits n_g photons per second uniformly in all directions, with all the photons of frequency f_ emitter an expression for the force on the sail if all the photons that strike it are reflected Assume that the sail has an area A. is located at a distance d from the star s center, is perpendicular to the incoming photons, and is momentarily at rest with respect to the star Form your expression in terms of the defined quantities, h (Planck's constant), and c (the speed of light) Find the force, in newtons acting on the starlight driven sail, using the following data for the star and the sail: n_8 = 2.3 times photons per second f_ = 680 THz A = 394.7 m^2 d = times 10^11 m F =Explanation / Answer
4. photons per scond = 0.80 x 3.9 x 10^41 photons
= 3.12 x 10^41 photons
energy per photon= h f = (6.626 x 10^-34) (680 x 10^12)
= 4.506 x 10^-19 J
total energy incident per second = 1.406 x 10^23 J/s
Force = P / c = (1.406 x 10^23)/(3 x 10^8)
= 4.685 x 10^14 N ...Ans
(b) F = 2 (4.685 x 10^14) = 9.372 x 10^14 N
(c) energy per photon = h f
Power = n1 h f
intensity at distance d = n1 h f / ( pi d^2)
Power absorbed = I A = n1 h f A / (pi d^2)
F = P / c = n1 h f A / (pi d^2 c )
(d) F = (2.5 x 10^65 x 6.626 x 10^-34 x 680 x 10^12 x 394.7 ) / (pi (1.7 x 10^11)^2 x 3 x 10^8)
F = 1.632 x 10^18 N
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