The magnetic field intensity vector of a plane wave is given by
$\overline{\mathrm{H}}(x, y, z, t)=10 \sin \left(50000 t+0.004 x+30 \; \hat{a}_{y}\right)$,
where $\hat{a}_{y}$ denotes the unit vector in $y$ direction.
The wave is propagating with a phase velocity
- $5 \times 10^{4} \mathrm{~m} / \mathrm{s}$.
- $-3 \times 10^{8} \mathrm{~m} / \mathrm{s}$.
- $-1.25 \times 10^{7} \mathrm{~m} / \mathrm{s}$.
- $3 \times 10^{8} \mathrm{~m} / \mathrm{s}$.