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Direction of Induced Electric Field

Physics Asked by Orpheus on April 21, 2021

I have a time dependent magnetic field $B(t)$ coming out of the plane. A charged particle (q) with some velocity v is placed in the the magnetic field, it will follow a certain path that is dictated by $$vec F= q(vec v times vec B)$$
It follows a circular path in the magnetic field.

My question is what does the induced electric field look like?

I understand this field is non conservative so probably will not have have the form of a radially outward field like the field from a stationary charge.

2 Answers

If the magnetic field has boundaries, then the induced electric field will form loops around the magnetic field. The size and shape of the loops will depend on the size and shape of the magnetic field and they will be centered on the effective center of the magnetic field.

Answered by R.W. Bird on April 21, 2021

Faradays Law in differential form states:

$$nabla times E = frac{- partial}{partial t}B$$

Since the definition of a conservative vector field $V$ is $V=nablaphi$ for some $phi$, and we know that $nabla times (nabla phi) = 0$ for all $phi$, we can state that a conservative vector field $V$ must obey the condition $nabla times V = 0$.

So therefore all electric fields are conservative, unless there is a time-varying magnetic field present.

From here we want to find $E$ given that we know its curl, and there is not a unique solution for this unless we have initial and boundary conditions for our magnetic and electric field. A simple way to think about this; if I just told you that $frac{- partial}{partial t}B =0$ can you use that to tell me $E$ uniquely? No. We need to know its I.C. and B.C. which would be dictated by charges, conductors, etc...

Answered by xXx_69_SWAG_69_xXx on April 21, 2021

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