Answer :

Explanation: A magnetic current can be produced by a moving


charge. If the charge is moving uniformly, it will generate a constant


current. If we assume a constant current is flowing through a


conductor of length L, the magnetic field due to it at a distance R


from it is given by Biot-Savart law. The field would be



where i is the constant current and μ0 is the magnetic permeability


of free space and its value is 4π × 10-7 T m A-1. So A. is correct.


A changing electric field can also generate a magnetic field around it. According to Ampere-Maxwell law, the total magnetic field around a region is due to flow of charge carriers (called as conduction current)


and the time varying electric flux. Mathematically


…(i)


where B is the magnetic field, dl is small element of length of an


Amperian loop, μ0 is the magnetic permeability of free space and its value is 4π × 10-7 T m A-1, Ienclosed is the current due to charge carriers (conduction current) and Id is the displacement current which


is related to changing electric field.


The displacement current is related to electric field as


…(ii)


where ϕE is the time varying electric flux through the surface


and ϵ0 is the electric permittivity of free space(vacuum) and is equal


to 8.85 × 10-12 C2 N-1 m-2.


The electric flux is the amount of electric field lines passing


through a surface normally. Mathematically


…. (iii)


where E(t) is the time varying electric field, dS are a small area


element on the surface and θ is the angle between the electric field


vector and area vector (if the field lines are not falling normally).


From (ii) and (iii)



If the conduction current is zero, so the magnetic field will entirely be


produced by the changing electric field and would be produced by it.


Hence B. is correct


Hence D. is correct

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