# Magnetic field and an electrical field

1. Nov 9, 2005

### Michael Lin

Hi all,
We know that if we have a current, we create a magnetic field and an electrical field. By the right hand rule, we can find the direction of the B, and E field. (ExB should give us the direction of the current). Now suppose we have electromagnetic induction. The B and E from before causes a local current. Is this local current still obey the E x B relation for direction?

Thanks,
Michael

2. Nov 11, 2005

### steve9983

Induction currents are generated by changes in magnetic flux. Magnetic flux is equal to the surface integral of B.da (<-- dot product). The direction of the new (local) current will be that which opposes a change of magnetic flux. The E and B fields created by this new current will obey all the same laws as any other situation.

Last edited: Nov 11, 2005
3. Nov 11, 2005

### pmb_phy

I'm a bit confused as to what electric field you're talking about.

A magnetic field that changes with time "creates" (i.e. its existance is simultaneous with) an electric field. Is that what you meant? If so then you can have a steady current creating a constant magnetic field. If you have a current carrying wire then inside the wire there is an electric field whose value is given by Ohms law. The value ExB does not always point in the direction of current flow. In fact in a straight wire with a steady current flowing in it ExB is perpendicular to the wire and hence the current. This gets into some very hairy physics and is best described by the article

Examples of Momentum Distributions in the Electromagnetic field and in Matter, W.H. Furry, Am. J. Phys., 37(6) June 1969

Pete