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# A high-powered laser beam

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A high power laser providing a nearly collimated beam with an average of 50 KW is used recently by the US Army as a weapon to shoot down a drone 3.6 km away. The laser beam diameter on the target is about 0.25-m after propagating such a distance.

(a) Find the average intensity at the target.
(b) Find the peak electric field E(max) and peak magnetic field B(max) of the beam at the target.
(c) Find the radiation pressure P when the laser beam is shining on the drone and is totally absorbed by the target?

https://brainmass.com/physics/applied-physics/high-powered-laser-beam-603664

## SOLUTION This solution is FREE courtesy of BrainMass!

a. Intensity,
I = P / Area = P/ (pi*d^2/4) = 50*10^3/(pi*0.25^2/4) = 1.02 MW m^-2

b. e0 = 8.86*10^-12 C^2/N/m^2
mu0 = 4pi *10^-7 T m/A

Intensity,
I = e0 * c * E^2 = c B^2 / mu0
=> E = sqrt (I/e0 * c) = sqrt (1.02*10^6 /(8.86*10^-12 *3*10^8)) = 19589.47 V m^-1

Emax = E*sqrt(2) = 27703.69 V m^-1

Bmax = Emax/c = 9.23*10^-5 Tesla

c. Pressure, P = e0*E^2 = 8.86*10^-12 * 19589.47^2 = 0.0034 N m^-2

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