Which effect of current can be utilised in detecting a current-carrying wire cancelled in a wall?

The three diagrams in the following figure shows the lines of force (field lines) between the poles of two magnets. Identify the poles A, B, C, D, E and F.

The figure given below shows the magnetic field between two magnets:

(i) Copy the diagram and label the other poles of the magnets.

(ii) Which is the weaker magnet?

What conclusion do you get from the observation that a current-carrying wire deflects a compass needle placed near it?

Name the scientist who discovered the magnetic effect of current.