The figure shows a long solenoid,a cylindrical coil of a number of turns of insulated copper wire,connected to a battery through an ammeter $A$ and a rheostat $Rh$.
$(i)$ Which end of the solenoid is a $N$-pole and which end is a $S$-pole?
$(ii)$ Draw the magnetic field lines inside the solenoid and indicate their directions. Are magnetic field lines closed?
$(iii)$ How can you increase the strength of the magnetic field inside the solenoid? Give two methods.

(N/A) $(i)$ Looking at end $P$,the current flows in a clockwise direction,therefore,$P$ acts as a south pole. Looking at end $Q$,the current appears to flow in an anti-clockwise direction,therefore,$Q$ acts as a north pole.
$(ii)$ Magnetic field lines inside a solenoid are shown in the figure. It is important to note that outside the solenoid,field lines are directed from the north pole to the south pole,but inside the solenoid,the field lines are directed from the south pole to the north pole. Yes,magnetic field lines are closed loops.
$(iii)$ The strength of the magnetic field inside a solenoid can be increased by:
$(a)$ Increasing the magnitude of the current flowing through the solenoid.
$(b)$ Increasing the number of turns of the copper wire in the solenoid.