**NEET Physics Notes Magnetic Effects of Current – Concept of Magnetic Field**

** Concept of Magnetic Field**

**Concept of Magnetic Field**

In 1820, Oersted observed that a compass needle suffers, a deflection when brought near a current carrying wire. This means that, electric current, that is electric charge in motion, gives rise to magnetism.

**Oersted’s Experiment**

Oersted found experimentally, that a magnetic field is established around a current carrying conductor just as it occurs around a magnet.

**Biot-Savart’s Law and its Applications**

According to Biot-Savart’s law, the magnetic field dB at a point P, due to a current element I dl is given by

Here,is a proportionality constant, having a value of **10 ^{_7}TmA^{_1} ** in free space.

The term is known as the magnetic permeability of free space, where . Dimensional formula for is

**[MLT**

^{-2}A^{-2}].Direction of magnetic field produced due to a current carrying straight wire can be obtained by the Right hand thumb rule.

According to right hand thumb rule grasp the wire carrying current in your right hand with your extended thumb pointing in the direction of current. Then, the fingers will curl around in the direction of the magnetic field.

**Magnetic Field due to Circular Current Loop**

If there is a circular coil of radius R and N number of turns, carrying a current / through the turns, then magnetic field at the centre of coil is given by

If there is a circular arc of wire subtending an angle θ at the centre of arc, then the magnetic field at the centre point

At a point O situated at a distance r from centre of a current carrying circular coil along its axial line. The magnetic field is