[Physics] On the shape of magnetic and electric fields in an electromagnetic wave

electromagnetic-radiation

Electromagnetic waves are generally depicted like this:

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Where the electric fields and magnetic fields exist in the planes perpendicular to the direction of propagation. I also realize that as the electric field changes while the wave is propagating, a magnetic field is induced and vice versa (by faraday's and maxwell's laws of induction). But, those laws predict that the fields will be circular. So, won't the electric and magnetic fields look different? Won't they be circles along arrows that are drawn in the figure? I haven't seen anything written about this anywhere.

Best Answer

You write the integral formulation of Faraday's law, but there is also the equivalent differential formalism: $$ \nabla\times\mathbf E=-\frac{\partial\mathbf B}{\partial t}\tag{1} $$ which can be proven in a straight-forward manner (and ought to be done in your standard E&M textbooks).

Using standard planar waves equations, $$ E_y=E_0\sin\left(kx-\omega t\right) \\ B_z=B_0\sin\left(kx-\omega t\right), \\ $$ then Equation (1) gives us that $$ kE_0\cos(kx-\omega t)=\omega B_0\cos(kx-\omega t) $$ Which enforces the well-known relation that $E_0=cB_0$. So clearly plane waves do satisfy Faraday's law.

A similar situation exists with Ampere's law, usually written as $$ \oint\mathbf B\cdot d\mathbf l=\frac{1}{c^2}\frac{d\phi_E}{dt} $$ which leads to $$ \nabla\times\mathbf B=\frac{1}{c^2}\frac{\partial\mathbf E}{\partial t} $$ (I'm ignoring the current density here).

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