Question

A laser emits 1.42 1018 photons per second in a beam of light that has a diameter of 1.82 mm and a wavelength of 524.0 nm. Determine each of the following for the electromagnetic wave that constitutes the beam.
(a) the average electric field strength


(b) the average magnetic field strength
S=Energy per unit time/Area = Nhf/A= =4Nhc/πD²λ=
=4•1.42•10¹⁸•6.63•10⁻³⁴•3•10⁸/π•(1.82•10⁻³)²•524•10⁻⁹=
=2.07•10⁵ W/m²
Electric field
E= sqrt{S/(ε₀c)}=
= sqrt{2.07•10⁵/8.85•10⁻²•3•10⁸}=8834 N/C
Magnetic field
B=E/c =8834/3•10⁸ =2.94•10⁻⁵T
A laser emits a beam of light whose photons all have the same frequency. When the beam strikes the surface of a metal, photo-electrons are ejected from the surface. What happens if the laser emits twice the number of photons per second?

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