How Much Energy Does a 3.5 mW He-Ne Laser Beam Carry Over 1 Meter?

[sgoeke]

Homework Statement

Determine the amount of energy carried in 1 m of a 3.5 mW He-Ne laser beam if the cross-sectional area of the beam is 5x10^-6 m^2.

Homework Equations

J/s = Watt

The Attempt at a Solution

I converted the mW to W. I feel like I should put .0035W over 5x10^-6 m^2 to get intensity. But I don't know where intensity comes into this problem or where the other 1 m comes in.

 

[berkeman]

Homework Statement

Determine the amount of energy carried in 1 m of a 3.5 mW He-Ne laser beam if the cross-sectional area of the beam is 5x10^-6 m^2.

Homework Equations

J/s = Watt

The Attempt at a Solution

I converted the mW to W. I feel like I should put .0035W over 5x10^-6 m^2 to get intensity. But I don't know where intensity comes into this problem or where the other 1 m comes in.

What is energy in terms of power and time? How long does it take light to travel 1 meter?

And remember that sometimes in problems, you may not need everything that you are given...