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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.
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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.

Answer

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 \(B_o=\sqrt 2B_{\mathit{rms}}=1.4\times 10^{-8}T\)
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