What constitutes the field of a magnet?

At the centre of which of the following four circular rings has the maximum magnetic field while passing equal current through each of them?

How does a current-carrying solenoid behave?

With the help of a neat diagram,describe how you can generate induced current in a circuit.

$A$ magnetic compass needle is placed in the plane of paper near point $A$ as shown in the figure. In which plane should a straight current-carrying conductor be placed so that it passes through $A$ and there is no change in the deflection of the compass? Under what condition is the deflection maximum and why?

$A$ student performs an experiment to study the magnetic effect of current around a current-carrying straight conductor. He reports that:
$(i)$ The direction of deflection of the north pole of a compass needle kept at a given point near the conductor remains unaffected even when the terminals of the battery sending current in the wire are interchanged.
$(ii)$ For a given battery,the degree of deflection of a $N$-pole decreases when the compass is kept at a point farther away from the conductor.
Which of the above observations of the student is incorrect and why?