Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Dimensions of Larmor formula

  1. Nov 21, 2008 #1
    The Larmor formula is:

    [tex]P=\frac{\mu_0 q^2 a^2}{6\pi c}[/tex]

    When I checked the units of this, I got [kg m^2 s^-1]. If it is in watts, shouldn't it be [kg m^2 s^-3]? I was pretty thorough in putting everything in SI units.

    [tex]\mu_0[/tex] is N/A^2 or kg m s^-2 A^-2.
    [tex]q^2[/tex] is C^2 or A^2 s^2
    [tex]a^2[/tex] is m^2 s^-2
    c is m s^-1

    Have I made a stupid error, or is this just the wrong way of doing the dimensional analysis?

    This is not homework.
  2. jcsd
  3. Nov 21, 2008 #2
    I don't think the formula is right.

    edit: Never mind. :P
    Last edited: Nov 21, 2008
  4. Nov 21, 2008 #3


    User Avatar
    Homework Helper
    Gold Member

    The units of acceleration are [itex]m/s^2[/itex] not [itex]m/s[/itex], so the units of [itex]a^2[/itex] are [/itex]m^2/s^4[/itex] not [/itex]m^2/s^2[/itex].
  5. Nov 21, 2008 #4
    Stupid error it is then, thanks :P. You'd think after 4 years of uni I might be able to get that one right...
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook