7
$\begingroup$

From what I have read, bremsstrahlung is caused by electrons loosing kinetic energy when being decelerated by another charged particle. The lost energy being converted into radiation.

So why isn’t bremsstrahlung produced when inducing current in a conductor for example? Is the electron velocity not high enough?

Obviously the answer is simple but I do not have an academic background in physics.

$\endgroup$

2 Answers 2

8
$\begingroup$

Electromagnetic radiation requires acceleration, which does not occur for a constant current in a wire. If the current is oscillating, there will be radiation, but it is not considered bremsstrahlung which is radiation resulting from a collision with another particle or a number of particles.

$\endgroup$
1
  • 2
    $\begingroup$ This is not correct. If the electron is classical, then even if it is moving in a straight line, it should keep accelerating and decelerating as they pass by ions. The true answer is that the electrons are quantum particles and the entire solid obeys quantum theory. $\endgroup$ Mar 3 at 18:20
1
$\begingroup$

For an AC or DC current in a metal wire, the electrons are accelerating mainly due to scattering processes at the atomic level -- even in a radio-frequency AC circuit, the time-scale for the acceleration due to the modulation of the current is so long that you can effectively think of it as DC for purposes of estimating Bremsstrahlung.

So the real question is why we don't see Bremsstrahlung due to collisions with atoms and impurities and such. The first thing to realize is that if this type of Bremsstrahlung does exist, then it will be infrared or optical-frequency radiation, not x-rays, because the electrons have eV energies, not keV energies as in an x-ray tube at the dentist's office.

And then there is the scaling of the radiation with acceleration. For deceleration in a straight line, the power emitted as Bremsstrahlung, in the nonrelativistic limit, goes like (K/x)^2, when a charge with an initial energy K is decelerated over a distance x. The mean free path of an electron in a copper wire might be on the order of a nanometer, while for 60 kV electrons in an x-ray tube, it will be quite a bit longer, maybe on the order of 10 μm. However, the energies differ by a factor of 6x10^4, and when you square that, it becomes a huge factor.

$\endgroup$
1
  • $\begingroup$ This helped a lot! So do it understand correctly that you say one reason is electron velocity is general lower in everyday circuits, than (obviously) in bremm causing electrons? $\endgroup$ Mar 4 at 16:02

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.