Evaluate the amplitude of electric and magnetic field produced by the radiation coming from a `20 pi` W bulb `20%` and it is a point source.

Explanation

Consider the situation shown below,

Intensity at distance r from a point source (bulb) `I = (P)/(4pir^(2))`
Efficiency, `eta = ("Output")/("Input") = (P)/(P')`
`rArr P = etaP' = ((20)/(100)) (20pi) = 4piW`
`I = (P)/(4pir^(2)) = (4pi)/(4pi(2)^(2)) = (1W)/(4m^(2)) = 0.25 W//m^(2)`
Also, intensity of EM wave is given by,
`I = 1/2 epsi_(0)E_(0)^(2)c`
`rArr 1/4 = 1/2 epsi_(0)E_(0)^(2) xx 3 xx 10^(8)`
`rArr E_(0)^(2) = (10^(-8))/(6epsi_(0)) = (10^(-8))/(6 xx 8.85 xx 10^(-12)) = (10^(4))/(6 xx 8.85)`
`:.` Amplitude of electric field , `E_(0) = (100)/(sqrt(6 xx 8.85)) = 13.73 V//m`
Amplitude of magnitude filed, `B_(0) = (E_(0))/(c) = (13.73)/(3 xx 10^(8)) = 4.57 xx 10^(-8) T`