Q. The electric field (in $NC^{- 1}$) in an electromagnetic wave is given by $E = 50\sin\omega(t - x/c)$. The energy stored in a cylinder of cross-section 10 ${cm}^{2}$ and length 100 cm, along the $x$-axis will be
A) $5.5 \times 60^{- 12}\ J$
B) $1.1 \times 10^{- 11}\ J$
C) $2.2 \times 10^{- 11}\ J$
D) $1.65 \times 10^{- 11}\ J$
Explanation
(b) Energy contained in a cylinder
$U =$ avearge energy density $\times$ volume
$= \frac{1}{2}\varepsilon_{0}E_{0}^{2} \times Al$
$= \frac{1}{2} \times \left( 8.85 \times 10^{- 12} \right) \times (50)^{2} \times \left( 10 \times 10^{- 4} \right) \times 1$
$= 1.1 \times 10^{- 11}\ J$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.