What is the shape of magnetic field lines around a straight current-carrying conductor?

What is the coil-like structure made of insulated copper wire wound in a cylindrical shape called?

If a circular loop is made of $6$ closely wound turns instead of a single turn,the magnetic field produced at the center of the loop becomes $.........$ times stronger.

The magnetic field at the center of a circular loop carrying an electric current is inversely proportional to $..........$.

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?