Calculate the electric and magnetic fields amplitude in an electromagnetic wave radiate by a 200 W bulb at a distance 2 m from it assuming efficiency of bulb is 5% and it behave like a point source.

Explanation

Effective power of the bulb `P = (5)/(100) xx 200= 10` watt
Intensity at distance r is given by
`l= (P)/(4 pi r^2)`
`= (10 )/(4 xx 3.14 xx 2^2 ) ("watt")/(m^2)`
`= (10)/(16xx 3.14) ("watt")/(m^2)`
`= 0.199 ("watt")/(m^2)`
`=0.2 ("watt")/(m^2)`
`l = (1)/(2) epsilon_(0) E_(0)^(2) c`
`E_(0)^(2) = (2l )/(c xx E_(0))`
`E_(0) = sqrt((2l)/(c xx epsilon_(0))`
`E_(0) sqrt((2xx 0.2)/(3 xx 10^(6) xx 8.85 xx 10^(-12))`
`E_0 = 12.27 (N)/(C )`
`B_(0) (E_0)/( C) = (12.27)/(3 xx 10^(8) ) = (12.27)/(3) xx 10^(-8) T`
`= 4.09 xx 10^(-6) T`