Pat\'s engine works by shining two lasers onto either side of his ship. The lase

Question

Pat's engine works by shining two lasers onto either side of his ship. The laser coming from the left has a power of 100 mW, distributed over an area of 1.0 cm2 The laser coming from the right is made up of light with a wavelenth of 400 nm. a) How many photons per second must hit the object from the beam from the right to keep the ship in static equilibrium? b) If the beam from the right is also over an area of 1.0 cm2, what is its intensity? c) If Pat changed his ship such that the beam from the left was reflected instead of absorbed, what would be the net force on the ship?

Explanation / Answer

Here ,

a)

energy of 1 photon , E = h*3*10^8/wavelength

E = h * 3 *10^8 /400 *10^-9

E = 4.97 *10^-19 J

Number of photons per second = 100 *10^-3 /4.97 *10^-19

Number of photons per second = 2.012 *10^17

b)

Intensity , If = power/area

If = 100 *10^-3 /1 *10^-4

If = 1000 W/m^2

c)

Now,

force acting is F = 2 * h * 2.012 *10^17 /400 *10^-9

F = 6.67 *10^-10 N

net force on the ship is 6.67 *10^-10 N

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