A) \[8.4\times {{10}^{-8}}\hat{k}T\]
B) \[2.4\times {{10}^{-8}}\hat{k}T\]
C) \[7.4\times {{10}^{-6}}\hat{i}T\]
D) \[2.4\times {{10}^{-8}}\hat{j}T\]
Correct Answer: B
Solution :
Given, \[E=7.2\hat{j}\,V/m\] The magnitude of B is \[B=\frac{E}{C}=\frac{7.2\,V/m}{3\times {{10}^{8}}\,m/s}=2.4\times {{10}^{-8}}\,T\] E is along Y-direction and the wave propagates along X-axis. Therefore, B should be in a direction - perpendicular to both X and\[Y-\]axes. Using vector algebra \[\mathbf{E\times B}\]should be along X-direction. Since, \[(+\hat{j})\times (+\hat{k})=\hat{i},B\]is along Z-direction. Thus, \[B=24\times {{10}^{-8}}\hat{k}\,T.\]
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