In the given diagram a part of circular wire of radius a meter makes an angle alpha the centre direction of current flowing in it is as shown the value of magnetic field at the centre P will be

Magnetism is the result of electric charge motion.As soon as an electric charge moves, it creates a magnetic effect perpendicular to its direction of motion. This can be easily verified by the a magnetized nail. If a steel nail is placed inside a coil ( A coil is a piece copper wire wrapped around a cylinder) that is connected to a battery, the nail becomes a magnet. Since the nail itself is perpendicular to the surface of each loop of the coil; therefore, we can say that the current, or the motion of electric charges is perpendicular to the nail (magnetic field). See the figure shown below:The reason for naming the poles of the nailasNandSis that if a magnet is hung at its middle by a string, it turns and aligns itself toward almost the North and South poles of the Earth. The end pointing to the North is called its North pole and the other end pointing to the South pole is called the South pole of the magnet. The Geographic North and the Magnetic North are off by a few degrees however, and the position of the magnetic north changes slightly over years. The reason for the magnetic effect of the Earth is also the motion of charged particles. The molten metal at the core of the Earth is ionized and has a rotational motion parallel to the Equator creating a huge magnet whose field must be perpendicular to the Equator plane and therefore passes through the North pole and the South pole of the Earth.