Question

Which of the following are true about the energy of electromagnetic waves in free space?

		A.Doubling the intensity of an electromagnetic wave doubles the amplitude of the magnetic field.
		B.The instantaneous energy density of the magnetic field is $\frac{1}{2}\varepsilon_0&space;E^{2}$ .
		C.The average intensity of an electromagnetic wave is $\frac{cB^2}{\mu_0}$ .
		D..The time average of $cos^2(kx-\omega&space;t)$  is $\frac{1}{2}$ .

Answer 1

B.The instantaneous energy density of the magnetic field is $\frac{1}{2}\varepsilon_0&space;E^{2}$