Question

Mona was doing an experiment with a magnetic compass and a straight current-carrying wire. She observed that as she moved the compass away from the current-carrying wire, the deflection of the compass needle reduced. 

A. Explain why the deflection of the compass needle reduced as Mona moved away the compass needle from the current carrying wire. 

B. Mention one thing that could have changed in the circuit of the wire that could increase the deflection of the needle. 

C. Explain with reason what will be the direction of the magnetic field associated with the wire for the case described by the above figure.

Answer 1

A. Magnetic field strength is inversely proportional to the distance from the current carrying wire. Hence when Mona moved the compass away from the current carrying wire, the magnetic effect was less on it and hence the deflection was less.

B. Magnetic field strength is directly proportional to the current in the wire. So, Mona could increase the current in the circuit to observe a greater deflection in the compass needle.

C. The battery suggests that the current is going from top of the plane to the bottom of the plane. Using the right hand thumb rule we can say that the magnetic field will be clockwise.