Question

Choose the correct answer from the alternatives given.
The electric field associated with an electromagnetic wave in vacuum is given by $\stackrel{-}{E}=40cos(kz-6\times {10}^{8}t)\stackrel{\wedge }{i}$, where $E,z$ and $t$ are in volt per meter, meter and second respectively. The value of wave vector $k$ is:

• A. $2m^{-1}$
• B. $0.5m^{-1}$
• C. $6m^{-1}$
• D. $3m^{-1}$

Answer 1

The correct option is A $2m^{-1}$

Compare the given equation with $E=E_{0}cos(kz-\omega t)$
We get, $\omega =6\times {10}^8{s}^{-1}$
$\therefore Wavevector,k=\frac{\omega }{c}=\frac{6\times {10}^8{s}^{-1}}{3\times {10}^{8}m{s}^{-1}}=2m^{-1}$