Question

A 7.5 × 10¹⁴ Hz laser emits a 7.7-?s pulse, 5.0 mm in diameter, with a beam energy density of 0.51 J/m³. What is the amplitude of the electric field of the emitted waves?
(c = 3.00 × 10⁸ m/s, ?₀ = 4? × 10^-7 T ? m/A, ?₀ = 8.85 × 10^-12 C²/N ? m²)

A) 340 kV/m

B) 480 kV/m

C) 240 kV/m

D) 150 kV/m

E) 120 kV/m

Answer: A

Please show all steps.

Answer 1

Formula for beam energy density = Energy/volume u = u^bar v = u^bar (AL) Intensity I = u/At 1 /2 epsilon_0 E^2 c = JAL/AT 1 /2 epsilon_0 E^2 = u^bar E = squareroot 2U^bar/epsilon = squareroot 2(0.515/m^3)/8.85 times 106-12 E = 340 KV/m