A) \[8.4\times {{10}^{-8}}\widehat{\mathbf{k}}T\]
B) \[2.4\times {{10}^{-8}}\widehat{\mathbf{k}}T\]
C) \[7.4\times {{10}^{-6}}\widehat{\mathbf{i}}T\]
D) \[2.4\times {{10}^{-8}}\widehat{\mathbf{j}}T\]
Correct Answer: B
Solution :
Given,\[E=7.2\,\,\widehat{\mathbf{j}}\,\,V/m\] 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, \[(+\widehat{\mathbf{j}})\times (+\widehat{\mathbf{k}})=\widehat{\mathbf{i}}\]\[,B\]is along \[Z-\]direction. Thus, \[B=2.4\times {{10}^{-8}}\widehat{\mathbf{k}}T\]
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