Conceptual Questions Based on Moving Charges and Magnetism
Q.1. How is a magnetic field produced ?
Sol. A magnetic field can be produced by the following ways:
(i) by a magnet
(ii) by a current carrying conductor
(iii) by a moving charge and
(iv) by changing electric field.
Q.2. What is the nature of magnetic field produced by a current flowing in a straight conductor ? Name the rule to find the direction of magnetic field.
Sol. When current flows through a straight conductor, the magnetic field is circular i.e. the magnetic lines of force are in the form of concentric circles with the conductor as centre. The plane of the magnetic lines of force is perpendicular to the length of the conductor. The direction of magnetic lines of force can be given by Right hand thumb rule.
Q.3. The net charge in a current-carrying conductor is zero, even then it experiences a force in a magnetic field. Why?
Sol. We know that a magnetic force acts on a charge moving in a magnetic field. In a conductor carrying current, the free electrons move towards the positive end of the conductor with some drift velocity hence magnetic force acts on them in a magnetic field. The positive ions of the conductor being stationary, do not experience any magnetic force.
Q.4. What is the nature of magnetic field produced by a current flowing in a circular wire loop. Name, the rule to find the direction of magnetic field.
Sol. When current flows through a circular wire loop, the magnetic field is nearly uniform near the centre of the circular wire. The magnetic lines of force are perpendicular to the wire loop and are circular near the wire and practically straight near the centre of the wire loop. If the radius of the current loop is very large, the magnetic field near the centre of the current loop is almost uniform. The direction of magnetic field at the centre of circular current loop is given by Right Hand Palm Rule.
Q.5. How will you identify whether the magnetic field at a point is due to the earth or due to some current carrying conductor ?
Sol. We know that a freely suspended magnetic needle always points in north-south direction due to earth’s magnetic field. If a freely suspended magnetic needle always rests in north-south direction, the magnetic field is due to earth, and if this magnetic needle turns to some other direction and returns back to north-south when the current is switched off, then the magnetic field is due to a current carrying conductor.