1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Electromagnetic Waves Problem - Please Help

  1. Dec 8, 2005 #1
    A 200 MW laser pulse is focused with a lens to a diameter of 2.0 micrometers.

    Part A:
    What is the laser beam's electric field amplitude at the focal point?

    Part B:
    What is the ratio of this electric field to the electric field that keeps the electron bound to the proton of a hydrogen atom? The radius of the electron's orbit is 0.053 nm.

    I was able to get Part A correct. I used I = P/A to find the intensity using the power and area and then used E = sqrt( (2* I) / (c * epsilon_0)) to find the amplitude of the electric field and I got a numerical value of 2.19×10^11 V/m.

    Part B is where I need help. I tried finding the electric field like I did in part A using the new radius given (0.053 nm) and then divided my answer from part A by this to get the ratio, but this does not work. What am I doing wrong?
  2. jcsd
  3. Dec 8, 2005 #2

    Chi Meson

    User Avatar
    Science Advisor
    Homework Helper

    You got the hard part! Part B is much simpler. Use the standard electric field equation for a point charge: E=q/(4pi epsilon r^2)
  4. Dec 8, 2005 #3
    thanks for the help.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook