A 20 W laser beam, with 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 intensity of the beam? A) 20 × 10⁶ W/m² B) 6.4 × 10⁶ W/m² C) 3.2 × 10⁶ W/m² D) 2.0 × 10⁵ W/m² E) 1.0 × 10⁵ W/m²

Question

Quizplus · Accepted Answer

The initial intensity is calculated using the formula I = P/A, where P is the power and A is the area. The initial area A = π(d/2)^2 = π(0.002/2)^2 m². Thus, I = 20 W / (π(0.001)^2) = 6.4 × 10^6 W/m².

A 20 W Laser Beam, with an Initial Diameter of 2.0