If the key in the arrangement (Figure) is taken out (the circuit is made open) and magnetic field lines are drawn over the horizontal plane $ABCD$,the lines are

When an electric current flows through a conducting wire,what is produced in the region around it?

$(a)$ Explain any three properties of magnetic field lines.
$(b)$ Give two uses of magnetic compass.

Draw a rough sketch of the pattern of the magnetic field lines due to:
$(i)$ current flowing through a circular coil,and
$(ii)$ a current-carrying solenoid.

What is the principle of an electric motor?

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.