A 100 W electric bulb produces electromagnetic radiation with electric field amplitude of `(2V)/(m)` at a distance of 10 m.
Assuming it as a point source, estimate the efficiency of the bulb. 

Options

A. 0.049
B. `2.5%`
C. `6.6%`
D. `19.7%`

Explanation

Intensity `=("power" xx eta)/(A) " "…(1)`
We know
`(1)/(2) I = (1)/(2) varepsilon_(0) E^2 c`
`I = (8.854 xx 10^(-12) ) (2^2 ) ( 3xx 10^8)`
`I = 0.0106 w//m^2 " "…(2)`
On subsitituting (2) in (1),
`0.0106 = ( 100xx eta)/( 4 xx pi xx (10^2))`
`rArr eta = 0.133 = 13.3%`