Question

An electromagnetic wave with frequency $\omega$ and wavelength $\lambda$ travels in the $+ y$ direction. Its magnetic field is along + x-axis. The vector equation for the associated electric field (of amplitude $E_0$) is

• A. $\vec{E}=-E_{0}\,cos\left(\omega t+\frac{2\pi}{\lambda}y\right)\hat{x}$
• B. $\vec{E}=E_{0}\,cos\left(\omega t-\frac{2\pi}{\lambda}y\right)\hat{x}$
• C. $\vec{E}=E_{0}\,cos\left(\omega t-\frac{2\pi}{\lambda}y\right)\hat{z}$
• D. $\vec{E}=-E_{0}\,cos\left(\omega t+\frac{2\pi}{\lambda}y\right)\hat{z}$

Answer 1

Answer: (C)

In an electromagnetic wave electric field and magnetic field are perpendicular to the direction of propagation of wave. The vector equation for the electric field is
$\vec{E}=E_{0}\,cos\left(\omega t-\frac{2\pi}{\lambda}y\right)\hat{z}$