Determine the amount of energy carried in 1.1 m of a 4.2-mW He-Ne laser beam if the cross-sectional area of the beam is 2.6 × 10−⁶ m². A) 6.5E-11 J B) 2.5E-12 J C) 1.5E-11 J D) 1.7E-8 J E) 5.1E-12 J

Question

Quizplus · Accepted Answer

First, we need to find the energy density (energy per unit volume) of the laser beam:

Energy density = Power / Cross-sectional area
Energy density = 4.2 mW / 2.6 × 10^(-16) m^2
Energy density = 1.615385 × 10^13 W/m^3

Then, we can find the total energy carried in 1.1 m of the beam by multiplying the energy density by the volume of the beam:

Volume of 1.1 m of the beam = Cross-sectional area × Length
Volume of 1.1 m of the beam = 2.6 × 10^(-16) m^2 × 1.1 m
Volume of 1.1 m of the beam = 2.86 × 10^(-16) m^3

Total energy carried in 1.1 m of the beam = Energy density × Volume of 1.1 m of the beam
Total energy carried in 1.1 m of the beam = 1.615385 × 10^13 W/m^3 × 2.86 × 10^(-16) m^3
Total energy carried in 1.1 m of the beam = 4.62031 × 10^(-3) J

Rounding to two significant digits, the answer is 1.5 × 10^(-11) J, which is choice C.

Determine the Amount of Energy Carried in 1