Home/Class 12/Physics/

Calculate the electric and magnetic fields produced by the radiation coming from a $$100\;W$$  bulb at a distance of $$3\;m$$ . Assume that the efficiency of the bulb is $$2.5$$  and it is a point source.
Speed
00:00
07:33

## QuestionPhysicsClass 12

Calculate the electric and magnetic fields produced by the radiation coming from a $$100\;W$$  bulb at a distance of $$3\;m$$ . Assume that the efficiency of the bulb is $$2.5$$  and it is a point source.

The radiation which comes out of the spherical area is directly proportional to the area
$$4\pi r^2=4\pi \times 3\times 3=113m^2$$
We know that intensity = $$\frac{\text{Power}}{\text{Area}}$$
Here in this question we have $$25$$ of the total power
So power used $$=25W$$
$$\text{Intensity}=\frac{25}{113}=0.022\frac W{m^2}$$
Half of this intensity calculated will be provided by $$E$$  and half by $$B$$
$$\frac 1 2I=\frac 1 2\upsilon _oE^2$$
$$E_{\mathit{rms}}=2.9V$$
$$E_o=\sqrt 2E_{\mathit{rms}}=\sqrt 2\times 2.9=4.07\frac V m$$
$$\text{Magnetic field}=\frac{E_{\mathit{rms}}} c$$
where $$c$$  is the speed of light.
$$B_{\mathit{rms}}=9.6\times 10^{-9}T$$
And $$B_o=\sqrt 2B_{\mathit{rms}}=1.4\times 10^{-8}T$$