A red LED emits light at 0.1 watt uniformly around it. The...

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 $1 \mathrm{~m}$ from the diode is [2015] (A) $2.45 \mathrm{~V} / \mathrm{m}$ (B) $5.48 \mathrm{~V} / \mathrm{m}$ (C) $7.75 \mathrm{~V} / \mathrm{m}$ (D) $1.73 \mathrm{~V} / \mathrm{m}$

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 $1 \mathrm{~m}$ from the diode is [2015]
(A) $2.45 \mathrm{~V} / \mathrm{m}$
(B) $5.48 \mathrm{~V} / \mathrm{m}$
(C) $7.75 \mathrm{~V} / \mathrm{m}$
(D) $1.73 \mathrm{~V} / \mathrm{m}$

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Key Concepts

Electromagnetic Wave Intensity

This concept refers to the power per unit area carried by a wave. When a source emits a known power uniformly, the intensity at a distance is calculated by dividing that power by the surface area over which the energy is spread. This forms the basis for understanding how energy density decreases with distance from the source.

Spherical Spreading

Spherical spreading describes the phenomenon where energy emitted isotropically from a point source is distributed equally over the surface of a sphere. Since the surface area of a sphere increases with the square of the radius, the intensity of the radiation diminishes as one moves farther from the source, following an inverse square law.

Poynting Vector and Electric Field Amplitude Relationship

The Poynting vector represents the rate at which electromagnetic energy is transmitted through a unit area and is directly related to the square of the electric field amplitude. In free space, the relationship S = (1/2)?? c E?² connects the measurable intensity to the amplitude of the electric field, allowing one to calculate the field strength from known power and distance.

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