A red LED emits light at $0.1 W$ uniformly around it. The amplitude of the electric filed of the light at a distance of $1 m$ form the diode is:

1.73 V / m

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2.45 V / m

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5.48 V / m

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7.75 V / m

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Solution

The correct option is B $2.45 V / m$
Intensity: $I = \frac{P}{4 π r^{2}}$
But, $I = \frac{1}{2} ϵ_{0} E_{0}^{2} C$
$\Rightarrow \frac{1}{2} ϵ_{0} E_{0}^{2} C = \frac{P}{4 π r^{2}}$
$\Rightarrow E_{0}^{2} = \frac{2 P}{4 π ϵ_{0} r^{2} C} = \frac{2 \times 0.1 \times (9 \times 10^{9})}{1^{2} \times 3 \times 10^{8}} = 6$
$\Rightarrow E_{0} = \sqrt{6} = 2.45 V / m$

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A red LED emits light at 0.1 W uniformly around it. The amplitude of the electric filed of the light at a distance of 1 m form the diode is:

The correct option is B 2.45 V/mIntensity: I=P4πr2But, I=12ϵ0E20C⇒12ϵ0E20C=P4πr2⇒E20=2P4πϵ0r2C=2×0.1×(9×109)12×3×108=6⇒E0=√6=2.45V/m

A red LED emits light at $0.1 W$ uniformly around it. The amplitude of the electric filed of the light at a distance of $1 m$ form the diode is: