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I have four different situation and i want to learn what kind of field (electric or magnetic) each produces and which produces electomagnetic waves?

1)dc current flow in a conductor

2)ac current flow in a conductor

3)q charge moving v velocity

4)q charge with a accelleration

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1  
What do you want to know about electromagnetic waves? –  Joshua Nov 3 '13 at 22:19

1 Answer 1

1) DC-current will result in a constant magnetic field, the right hand rule can be used here. See https://en.wikipedia.org/wiki/Magnetic_field#Magnetic_field_and_electric_currents for more information on that. An electromagnetic wave is not "produced" in the steady state case, as we ignore the activation operation.

2) An AC-current will result in a alternating magnetic field. An alternating magnetic field will cause an alternating electrical field and voila - you just made an antenna and will send electromagnetic waves. Anyhow, its a very bad antenna, but there are a lot of tricks to make them better.

3) Is the same case as 1)

4) An accelerated charge will always result in bremsstrahlung, see https://en.wikipedia.org/wiki/Bremsstrahlung for more information on that.

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1  
Afaik, For 3 the result is not quite the same as a dc current flowing in a conductor, because of the spatial and temporal dependence of the magnetic field. The way to obtain the result is to Lorentz transform the Coulomb field into a frame where $q$ is moving with velocity $v$. I don't think $E$ vanishes in this case, unlike a conductor in which $E$ is zero. –  lionelbrits Nov 3 '13 at 22:59
    
Oh yes, you're right there. I overlooked the current is not continuous in this case. –  Fips Nov 3 '13 at 23:15

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