explain an activities to show that …

Magnetic Field due to a Straight Current-carrying Conductor:

The magnetic field lines around a straight conductor carrying a current are concentric circles. The direction of a magnetic field is given by the Right-Hand Thumb Rule.Take a magnetic needle pivoted at its centre and free to move in horizontal plane.
Take a thick and insulated copper wire PQ and connect it to the battery circuit through a key K and a variable resistance Rh.
Hold the wire PQ parallel and just above the axle of the magnetic needle and press the key. It is observed that N-pole of the needle points towards the west so long the current continues to flow through the wire. It is also observed that if the current is increased or decreased, the deflection of the magnetic needle also increases or decreases.
If the direction of the current through PQ is reversed, i.e., if the current flows from Q to P, then N-pole of the needle is deflected towards east, this experiment shows that a magnetic field is set up around a current carrying conductor.