Question

A time-varying magnetic field is caused by which of the following?

-current carrying wires carrying a constant current
-a positive test charge moving through a constant electric field
-fluctuating electric fields
-the interaction with earth’s magnetic field

Answer 1

A time-varying magnetic field can be caused by fluctuating electric fields.

Answer 2

-fluctuating electric fields

Step-by-step explanation:

As we know that electric field and magnetic field is related by the equation given as

`\int E. dl = -(d\phi)/(dt)`

here we know that

`\phi = B.A`

now we have magnetic field is time varying

`\int E.dl = -A(dB)/(dt)`

now for closed loop of radius "r" we will have

`E(2\pi r) = - A(dB)/(dt)`

`E = -(A)/(2\pi r)(dB)/(dt)`

so here this produce electric field as per above formula and it is also known as non conservative electric field.