If a 20 W laser beam,which has an initial diameter of 2.0 mm,spreads out to a diameter of 2.0 m after traveling 10,000 m,what is the initial E_rms of the beam? A) 4.9 $\times$ 10⁴ V/m B) 2.5 $\times$ 10³ V/m C) 1.2 $\times$ 10³ V/m D) 1.9 $\times$ 10² V/m E) 1.7 $\times$ 10² V/m

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Quizplus · Accepted Answer

The initial E_rms can be calculated using the formula E_rms = √(2P/(cε₀A)), where P is the power, c is the speed of light, ε₀ is the permittivity of free space, and A is the initial area of the beam. Substituting the given values, the initial E_rms is approximately 4.9 * 10⁴ V/m.

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