The flow of a current in a circular loop of wire creates a magnetic field at its centre. How may the existence of this field be detected? State the rule which helps to predict the direction of this magnetic field. 

A magnetic compass needle is placed in the plane of paper near point A as shown in Figure. In which plane should a straight current carrying conductor be placed so that it passes through A and there is no change in the deflection of the compass? Under what condition is the deflection maximum and why?

Under what conditions is permanent electromagnet obtained if a current carrying solenoid is used? Support your answer with the help of a labelled circuit diagram.

AB is a current carrying conductor in the plane of the paper as shown in Figure. What are the directions of magnetic fields produced by it at points P and Q? Given $r_{1 }> r_2$ where will the strength of the magnetic field be larger?