Question

The electric field in an electromagnetic wave is given by $E =56.5 \sin \omega( t - x / c ) NC ^{-1}$. Find the intensity of the wave if it is propagating along $x$-axis in the free space. (Given $\varepsilon_{0}=8.85 \times 10^{-12} C ^{2} N ^{-1} m ^{-2}$ )

• A. $5.65\, Wm ^{-2}$
• B. $4.24\, Wm ^{-2}$
• C. $1.9 \times 10^{-7} Wm ^{-2}$
• D. $56.5 \,Wm ^{-2}$

Answer 1

Answer: (B)

$I =\frac{1}{2} \varepsilon_{0} E _{0}^{2} c$
$I =\frac{1}{2} \times\left(8.85 \times 10^{-12}\right)(56.5)^{2} \times\left(3 \times 10^{8}\right)$
$ = 4.24\,Wm^{-2}$