An electron is on the z axis moving toward the xy plane but it has not reached t

Question

An electron is on the z axis moving toward the xy plane but it has not reached that plane yet. At that instant: there is only a true current through the xy plane there is only a displacement current through the xy plane there are both true and displacement currents through the xy plane there is neither a true nor a displacement current through the xy plane none of the above are true In the figure a uniform electric field is directed out of the page within a circular region of radius R = 3.50 cm. The magnitude of the electric field is given by E = (4.00 times 10^-3 V/m middot s) where t is in seconds. What is the magnitude of the magnetic field that is induced at radial distances (a) 2.50 cm and (b) 7.00 cm?

Explanation / Answer

12. There is only displacement current through x-y plane because net charge flowing at that time in any given cross section area is zero in x-y plane. so true current is zero.

correct answer is option B

14. C

Gauss's law for magnetism takes an analogous form,

B=0m

We also know that an electric current produces a magnetic field, so it must also be that a magnetic current produces an electric field in an analogous fashion. That is, we have to add a term proportional to the magnetic current into the Maxwell--Faraday law. By dimensional analysis the proportionality constant should be plus or minus unity. But how do we know which? Here we can appeal to Lenz's law. We know that an increasing magnetic field induces an electric field that drives current through a loop according to the left hand rule, so that the current produces an opposing magnetic field by the right hand rule. We suppose that an increasing electric field must induce an opposing electric field in a wire that conducts magnetic monopoles. Because a changing electric field induces a magnetic field according to the right hand rule, the magnetic current must produce an electric field according to the left hand rule. So we have this form of the Maxwell--Faraday law:

×E=JmB/t

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