Question

A magnetic field can be produced by
A. moving charge
B. A changing electric field
C. Both of these
D. None of these

Answer 1

Hint:Students should try to recall the condition to produce magnetic fields to solve this question. A magnetic field can be produced by both a moving charge which ultimately causes change in the electric field associated with it or a changing electric field.A charge moving in a magnetic field experiences a force mutually perpendicular to both velocity and the direction of magnetic field.

Complete answer:
 A charged particle that moves without acceleration produces both an electric field as well as a magnetic field. The electric field is due to the charge on the particle. When the particle moves the electric field associated with that particle changes and therefore induces a magnetic field. This particle cannot produce a magnetic field if at rest.
Also changing electric fields can produce a magnetic field and vice versa is also true which is indicated by faraday's law of induced current to give two changing magnetic fields. For example the current running in a circular loop produces a magnetic field along its Axis due to the change in the direction of the electric field. Therefore both moving charge and a changing electric field can produce magnetic fields.

Hence, option C is the correct answer.

Note:Students should keep in mind to prevent error in answer that a charge at rest cannot produce a magnetic field as there would be no change in electric field associated with it. So the answer should mention it specifically a moving charge particle and not only charge particle.The magnetic field is a region where a charge, a current carrying wire or any magnetising material can experience an influence due to magnetisation.