What is a solenoid?

What type of core is used to make an electromagnet?

$A$ constant current flows in a horizontal wire in the plane of the paper from east to west as shown in the figure. The direction of the magnetic field at a point will be North to South:

In the below figure,$A$ and $B$ represent two straight wires carrying equal currents in a direction at right angles to the plane of paper inwards. Sketch separately the magnetic field lines produced by each current. Give a reason why the magnetic field at $K$ (mid-point of the line joining $A$ and $B$) will be zero.
What will be the effect on the magnetic field at $K$ if the current in wire $B$ is reversed?

How will the magnetic field produced in a current-carrying circular coil change if we increase the:
$(i)$ value of current flowing through it?
$(ii)$ distance of point $P$ from the coil?
$(iii)$ number of turns of the coil?

According to Fleming's right-hand rule,what is indicated by the direction of the center finger?