1. An EM wave representing 650 nm laser light is traveling in the +zˆ direction. At one point in space and time, the electric field is in the +yˆ direction (i. s., the polarization of the wave is along the yˆ direction). Assume that the amplitude of the electric field is 20.0 V/m.

(a) At this same location in space/time, in what direction is the magnetic field pointing?
(b) What is the magnitude of the magnetic field?
(c) What is the magnitude of the average power per unit area of this wave?

Explanation:

a ) Direction of the magnetic field will be in positive x direction.

The direction of the vector E X B gives the direction of motion of wave.

b ) Magnitude of magnetic field is given by the relation

E₀ / B₀ = c , c is velocity of light

B₀ = E₀ / c

= 20 / (3 x 10⁸)

= 6.67 x 10⁻⁸ T

c ) Average power flowing per unit area by this wave is called Poynting vector

c ε₀E₀² , ε₀ = 8.85X10⁻¹²

= 3 X 10⁸ X 8.85 X 10⁻¹² X 20²

= 1.062 W m⁻²

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