# Electromagnetic waves

#### erisedk

1. Homework Statement
Calculate electric field and magnetic field produced by radiation emitted by a 100 W bulb at a distance of 1 m if radiation efficiency is only 5%.

2. Homework Equations

3. The Attempt at a Solution
I only know how to find intensity due to the bulb:
I = P/4πr2 = 5/4π W/m2
I have absolutely no idea how to find the electric and magnetic field from that information.
I do know that B = E/c, so I just need to find one of those.

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#### jtbell

Mentor
I have absolutely no idea how to find the electric and magnetic field from that information.
Look in your textbook (or Google) for an equation for the power (density) carried by an electromagnetic wave. It can be expressed in terms of either the electric or magnetic field. It's a standard equation so it should be in your book if it has that exercise.

#### erisedk

Got it, I = (εE^2)(c).
No, it's not a textbook problem. And my book doesn't have much on this.
Thanks!

#### jtbell

Mentor
Well, it sure looks like a textbook or exam problem. I've given similar problems to students many times. 