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## QuestionPhysicsClass 12

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?

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. $$b=2.1\times 10^{-8}\;kT.$$