A red L E D 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:

Question

A red L E D 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:, 7 . 75 V m - 1, 1 . 73 V m - 1, 2 . 45 V m - 1, 5 . 48 V m - 1

MARKS App · Accepted Answer

For a point source of power = P, then intensity at a point at a separation x from the source is, I = P o w e r A r e a = P 4 π x 2 ∵ The average intensity of E.M. wave is given by, I = 1 2 c ε 0 E o 2 ⇒ E 0 = 2 P 4 π ε 0 c x 2 ∵ 1 4 π ε 0 = 9 × 10 9 , P = 0.1 W , x = 1 m , c = 3 × 10 8 m s - 1 ⇒ E 0 = 2 × 0.1 × 9 × 10 9 3 × 10 8 × 1 2 = 6 = 2.45 V m - 1

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