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A plane electromagnetic wave of frequency \(25\;\mathit{MHz}\)  travels in free space along the \(x-\text{direction.}\)  At a particular polnt in space and time, \(E=6.3 \;J y/m.\) What is \(B\)  at this point?

Answer

Using Equation given below the magnitude of \(B\)  is
\(B=\frac E c\)
\(=\frac{3.3}{3\times 10^8}=2.1\times 10^{-8}\;T\)
To find the direction. we note that \(E\)  is along \(Y\text{-direction}\) and the wave propagates along \(X \text{-axis}.\) Therefore, \(B\) should be in a direction perpendicular to both \(X-Y\text{ axis.}\) Using vector algebra. \(E\times B\) should be along \(X\text{-direction}.\) Since, \(\text j\times +\text k=1,B\) is along the \(Z\text{-direction}.\) Thus. \(b=2.1\times 10^{-8}\;kT.\)
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