Proceeding from Maxwell's equations show that in the case of a plane electromagnetic wave (Fig. 4.38) propagating in vacuum the following relations hold: ∂E∂t=−c2∂B∂x,∂B∂t=−∂E∂x \frac{\partial E}{\partial t}=-c^{2} \frac{\partial B}{\partial x}, \quad \frac{\partial B}{\partial t}=-\frac{\partial E}{\partial x} ∂t∂E=−c2∂x∂B,∂t∂B=−∂x∂E