Question

A plane polarized monochromatic $EM $ wave is traveling in vacuum along $z$ direction such that at $t = t_1$ it is found that the electric field is zero at a spatial point $z_1$. The next zero that occurs in its neighbourhood is at $z_2$. The frequency of the electromagnetic wave is :

• A. $\frac{3 \times 10^8}{|z_2 - z_1|}$
• B. $\frac{1.5 \times 10^8}{|z_2 - z_1|}$
• C. $\frac{6 \times 10^8}{|z_2 - z_1|}$
• D. $\frac{1}{t_1 + \frac{|z_2 - z_1|}{3 \times 10^8}} $

Answer 1

Answer: (B)

Since $c=f \lambda \Rightarrow f=\frac{c}{\lambda}$.
Here, $\lambda=2\left|z_{2}-z_{1}\right|$ and $c=3 \times 10^{8} .$ Therefore,
$f=\frac{3 \times 10^{8}}{2\left|z_{2}-z_{1}\right|}=\frac{1.5 \times 10^{8}}{\left|z_{2}-z_{1}\right|}$