The electric field in an electromagnetic wave is given by \( \vec{E} = \hat{\imath} \, 40 \cos \omega \!\left( t - \frac{z}{c} \right) \, \text{N C}^{-1} \). The magnetic field induction of this wave is (in SI unit):
\( \vec{B} = \hat{\jmath} \, 40 \cos \omega \!\left( t - \frac{z}{c} \right) \)
\( \vec{B} = \hat{k} \, \frac{40}{c} \cos \omega \!\left( t - \frac{z}{c} \right) \)
\( \vec{B} = \hat{\jmath} \, \frac{40}{c} \cos \omega \!\left( t - \frac{z}{c} \right) \)
\( \vec{B} = \hat{\imath} \, \frac{40}{c} \cos \omega \!\left( t - \frac{z}{c} \right) \)