Related Formula
B₀ = (E₀)/(C)$$B_0 = \frac{E_0}{C}$$
C = E × B$$\hat{C} = \hat{E} \times \hat{B}$$
Core Logic
In an electromagnetic wave in free space, the magnitudes of the electric and magnetic fields are related by E₀ = c B₀$E_0 = c B_0$. Thus, B₀ = E₀ / C$B_0 = E_0 / C$.
The direction of wave propagation is given by the cross product of the electric field and magnetic field vectors: C = E × B$\hat{C} = \hat{E} \times \hat{B}$.
Step 1: Determine Wave Direction and Magnetic Field Direction
Given the phase term (ω t - kz)$(\omega t - kz)$, the wave propagates in the +z$+z$ direction, so C = k$\hat{C} = \hat{k}$.
The electric field oscillates in the +x$+x$ direction, so E = i$\hat{E} = \hat{i}$.
We know:
k = i × B$$\hat{k} = \hat{i} \times \hat{B}$$
Since i × j = k$\hat{i} \times \hat{j} = \hat{k}$, the magnetic field must oscillate in the +y$+y$ direction (j$\hat{j}$).
Step 2: Construct Final Vector
The full magnetic field vector shares the same phase and applies the above amplitude and direction:
B = (E₀)/(C) (ω t - kz) j$$\vec{B} = \frac{E_0}{C} \cos(\omega t - kz) \hat{j}$$
Pattern Recognition
Phase remains identical. Amplitude scales by 1/c$1/c$. Direction satisfies the right-hand triad ( E, B, v)$(\vec{E}, \vec{B}, \vec{v})$ where v = E × B$\vec{v} = \vec{E} \times \vec{B}$.
Chapter Mix
Class 12 Physics: Electromagnetic Waves