What is the unit of magnetic field strength?

The figure shows the magnetic field lines of a magnetic field. There are three points $A$, $B$ and $C$ in this field. Choose the correct option regarding field strength.

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

The diagram below shows a magnetic needle kept just below the conductor AB which is kept in the North-South direction.

i) In which direction will the needle deflect when the key is closed?

ii) Why is the deflection produced?

iii) What will be the change in the deflection if the magnetic needle is taken just above the conductor AB?

iv) Name one device which works on this principle.

Observe the given figure of Fleming' s Right Hand Rule and write the labels of A and B correctly.

Which of the following is NOT correct for magnetic filed lines?