Chat with tutor

Ask Questions, Get Answers

Questions  >>  JEEMAIN and NEET  >>  Physics  >>  Class12  >>  Electromagnetic Waves

According to electromagnetic wave theory, the electric and magnetic field vector associated with the wave is given by \[\] $|E| = E_{max} \cos(kx – \omega t)$ \[\] $|B| = B_{max} \cos(kx – \omega t)$ \[\] The energy of electromagnetic wave is confined in the form of electric and magnetic fields. The energy per unit volume in an electric field is given by $U_E = \large\frac{1}{2} \in_oE^2$ and the energy per unit volume in a magnetic field is given by $ U_M =\large\frac{1}{2} B^2/ \mu_0$ . The energy density associated with the magnetic field is equal to the energy density associated with the electric field. The total energy is equally shared by the electromagnetic as well as magnetic field. The rate of flow of energy in an electromagnetic wave is defined as pointing vector $S = 1/\mu_o (E \times B)$. A plane electromagnetic wave varies sinusoidally at $90\: MHz $ as it travels along the $+ve\: x$ direction. The peak value of the electric field is $2\: millivolt/m$ and it is directed along $ \pm y$ direction \[\] The average energy density in the radiation is

$\begin {array} {1 1} (a)\;1.5 \times 10^{-7} J/m^3 & \quad (b)\;1.75 \times 10^{-14} J/m^3 \\ (c)\;3 \times 10^{-12}J/m^3 & \quad (d)\;3 \times 10^{-14} J/m^3 \end {array}$

1 Answer

$u_E = \large\frac{1}{2}$$ \in_oE^2 = \large\frac{1}{2}$$ \times 8.85 × 10^{-12} \times (2 \times 10^{-3} )^2 = 1.75 \times 10^{-14} J/m^3$
Ans : (b)
Help Clay6 to be free
Clay6 needs your help to survive. We have roughly 7 lakh students visiting us monthly. We want to keep our services free and improve with prompt help and advanced solutions by adding more teachers and infrastructure.

A small donation from you will help us reach that goal faster. Talk to your parents, teachers and school and spread the word about clay6. You can pay online or send a cheque.

Thanks for your support.
Please choose your payment mode to continue
Home Ask Homework Questions
Your payment for is successful.
Clay6 tutors use Telegram* chat app to help students with their questions and doubts.
Do you have the Telegram chat app installed?
Already installed Install now
*Telegram is a chat app like WhatsApp / Facebook Messenger / Skype.