Question

An electromagnetic wave of frequency $1\times {10}^{14}$ hertz is propagating along z - axis. The amptitude of electric field is 4 V/m. If ${ϵ}_0=8.8\times {10}^{-12}{C}^2/N-m^2$, then average energy density of electric field will be:

• A. $35.2\times {10}^{-13}J/m^3$
• B. $35.2\times {10}^{-12}J/m^3$
• C. $35.2\times {10}^{-11}J/m^3$
• D. $35.2\times {10}^{-10}J/m^3$

Answer 1

The correct option is B $35.2\times {10}^{-12}J/m^3$

${\mu }_{av}=\frac{1}{4}{ϵ}_0{E}^2=\frac{1}{4}\times 8.8\times {10}^{-12}\times 4^2$
$=8.8\times {10}^{-12}\times 4$
$=35.2\times {10}^{-12}J/m^3$