Question

The electric field (in $N\, C^{-1}$) in an electromagnetic wave is given by $E=50\,sin\,\omega\left(t-\frac{x}{c}\right).$ The energy stored in a cylinder of cross-section $10\, cm^2$ and length $100\, cm$ along the x-axis will be

• A. $5.5 × 60^{-12}\, J$
• B. $1.1 × 10^{-11}\, J$
• C. $2.2 × 10^{-11}\, J$
• D. $1.65 × 10^{-11}\, J$

Answer 1

Answer: (B)

Energy contained in a cylinder
U = average energy density × volume
$=\frac{1}{2}\varepsilon_{0}E^{2}_{0}\times Al$
$=\frac{1}{2}\times\left(8.85\times10^{-12}\right)\times\left(50\right)^{2}\times\left(10\times10^{-4}\right)\times1$
$=1.1\times10^{-11}\,J$