Magnitude of an electromagnetic wave is `E=4.24 sin [(7.54xx10^(6))(t-(x)/(3xx10^(8)))](mV)/(m)`.
Then energy density associated with magnetic field of this wave is …….
(a) `796xx10^(-19) J`
(b) `796xx10^(-19) J//m^(3)`
(c) `7.96xx10^(-19) J//m^(3)`
(d)`796xx10^(-19) W`

Options

A. `796xx10^(-19)J`
B. `796xx10^(-19)J//m^(3)`
C. `7.96xx10^(-19)J//m^(3)`
D. `796xx10^(-19)W`

Answer

B

Explanation

Here, `E_(m)=4.24(mV)/(m)`
`therefore E_(rms)=(E_(m))/(sqrt(2))=(4.24)/(1.414)=2.998 (mV)/(m)`
`therefore E_(rms)~~ 3xx10^(-3)(V)/(m)`
Now energy density,
`rho = epsilon_(0)E_(rms)^(2)`
`=8.85xx10^(-12)xx(3xx10^(-3))^(2)`
`= 7.9.65xx10^(-18)~~ 796xx10^(-19)J//m^(3)`