A helium-neon laser of the type often found in physicslaboratories has a beam po

Question

A helium-neon laser of the type often found in physicslaboratories has a beam power of 2.50 mW at a wavelength of 633 nm.The beam is focused by a lens to a circular spot whose effectivediameter may be taken to be equal to 2.00 wavelengths.
A) Calculate the intensity of the focused beam. B) Calculate the radiation pressure exerted on atiny perfectly absorbing sphere whose diameter is that of the focalspot.
C) Calculate the force exerted on thissphere. D) Calculate the magnitude of the accelerationimparted to it. Assume a sphere density of4.70×103kg/m3
A helium-neon laser of the type often found in physicslaboratories has a beam power of 2.50 mW at a wavelength of 633 nm.The beam is focused by a lens to a circular spot whose effectivediameter may be taken to be equal to 2.00 wavelengths.
A) Calculate the intensity of the focused beam. B) Calculate the radiation pressure exerted on atiny perfectly absorbing sphere whose diameter is that of the focalspot.
C) Calculate the force exerted on thissphere. D) Calculate the magnitude of the accelerationimparted to it. Assume a sphere density of4.70×103kg/m3
C) Calculate the force exerted on thissphere. D) Calculate the magnitude of the accelerationimparted to it. Assume a sphere density of4.70×103kg/m3

Explanation / Answer

(a)    the intensity is given by    I = P / ( d2 / 4)      = ........... W / m2 (b)    the radiation pressure is    pr = I / c         = .........Pa (c)    the force exerted will be    Fr = (P / I) pr        = ......... N (d)    the acceleration of the sphere will be    a = Fr / m       = ......... m /s2

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