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A red LED emits light a 0.1 watt uniform...

A red LED emits light a 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

A

1.73 V/m

B

2.45 V/m

C

5.48 V/m

D

7.75 V/m

Text Solution

Verified by Experts

The correct Answer is:
B
Intensity of light at a distance r, `I=P/(4pir^2)` [P=power]
Again, if the amplitude of the electric field is `E_0` ,
then `I=1/2cin_0E_0^2`
`therefore P/(4pir^2)=1/2cin_0E_0^2`
or , `E_0=sqrt((P)/(2picin_0r^2))`
`=sqrt((0.1)/(2xx3.14xx(3xx10^8)xx(8.85xx10^(-12))xx1^2))`
=2.45 V/m
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