Question

Find the energy contained in a cylinder of cross section $10{cm}^2$ and length $50cm$ along x-axis, if $E=50\sin \omega (t-x/C)$ be the electric field in an electromagnetic wave

• A. $5.5\times {10}^{-12}J$
• B. $1.5\times {10}^{-11}J$
• C. $6.2\times {!0}^{-10}J$
• D. $1.1\times {10}^{-15}J$

Answer 1

The correct option is A $5.5\times {10}^{-12}J$

Energy density, $U_{av}=\frac{1}{2}{\epsilon }_0{E}_0^2$

$=\frac{1}{2}\times 8.85\times {10}^{-12}\times {50}^2$ = $1.1\times {10}^{-8}J/m^3$

Volume, $V=10\times 50=5\times {10}^{-4}{m}^3$

So, energy $=U_{av}XV=5.5\times {10}^{-12}J$