A Red LED emits light 0.1 watt uniformly around it. The amplitude of the electric field of the light at a distance of 1 m from the diode is :

Options

A. (A) 1.73 V/m
B. (B) 2.45 V/m
C. (C) 5.48 V/m
D. (D) 7.75 V/m

Answer

B

Explanation

`I=(E )/(At)=(P)/(A)=(P)/(4pi r^(2))`
`rho c=(P)/(4pi r^(2))[because I =rho c]`
`(1)/(2)in_(0)E_(0)^(2)c=(P)/(4pi r^(2))`
`therefore E_(0)^(2)=(2P)/(4pi r^(2)in_(0)c)`
`therefore E_(0) sqrt((2P)/(4pi r^(2)in_(0)c))`
`= sqrt((2xx0.1xx9xx10^(9))/((1)^(2)xx3xx10^(8)))`
`= sqrt((18)/(3))=sqrt(6)=2.449 V//m ~~ 2.45 V//m`