Question
A red LED emits light at 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:
-
1.73 V/m
-
2.45 V/m
-
5.48 V/m
-
7.75 V/m
Solution
B.
2.45 V/m
Consider the LED as a point source of light.
Let power of the LED is P
Intensity at r from the source
... (i)
As we know that,
.... (ii)
From eqs. (i) and (ii) we can write
