A plane polarized monochromatic EM wave is travelling in a vacuum along $z$ direction such that at $\mathrm { t } = \mathrm { t } _ { 1 }$ 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: (1) $\frac { 3 \times 10 ^ { 8 } } { \left| z _ { 2 } - z _ { 1 } \right| }$ (2) $\frac { 6 \times 10 ^ { 8 } } { \left| z _ { 2 } - z _ { 1 } \right| }$ (3) $\frac { 1.5 \times 10 ^ { 8 } } { \left| z _ { 2 } - z _ { 1 } \right| }$ (4) $\frac { 1 } { t _ { 1 } + \frac { \left| z _ { 2 } - z _ { 1 } \right| } { 3 \times 10 ^ { 8 } } }$
A plane polarized monochromatic EM wave is travelling in a vacuum along $z$ direction such that at $\mathrm { t } = \mathrm { t } _ { 1 }$ 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:\\
(1) $\frac { 3 \times 10 ^ { 8 } } { \left| z _ { 2 } - z _ { 1 } \right| }$\\
(2) $\frac { 6 \times 10 ^ { 8 } } { \left| z _ { 2 } - z _ { 1 } \right| }$\\
(3) $\frac { 1.5 \times 10 ^ { 8 } } { \left| z _ { 2 } - z _ { 1 } \right| }$\\
(4) $\frac { 1 } { t _ { 1 } + \frac { \left| z _ { 2 } - z _ { 1 } \right| } { 3 \times 10 ^ { 8 } } }$