**NEET Physics Notes Magnetic Effects of Current-Ampere’s Circuital Law**

**Ampere’s Circuital Law**

According to Ampere’s circuital law, the line integral of the magnetic field B around any closed path is equal to times the net current I threading through the area enclosed by the closed path. Mathematically,

Now, consider the diagram below

**Applications of Ampere’s law**

The followings are the few important applications of Ampere’s law may be given as

**Magnetic field due to Straight Current Carrying Wire**

The magnetic field due to a current carrying wire of finite length at a point P situated at a normal distance r is From Ampere’s law,

When point P lies on axial position of current carrying conductor, then magnetic field at P, B = 0

**Magnetic Field due to a Thick (Cylindrical) Wire**

Let us have a thick cylindrical wire of radius R and infinite length, which carries a current I. Then,

magnetic field at a point outside the wire where, r is the distance of given point from centre of wire and r> R.

Magnetic field at a point inside the wire at a distance r from centre of wire (r < R) is

Magnetic field inside a hollow current carrying conductor is zero.

**Magnetic Field due to a Solenoid**

A current carrying solenoid behaves as a bar magnet. The face, where current is flowing clockwise behaves as South pole and the face, where current is seen flowing anti-clockwise, behaves as North pole.

For such a solenoid, the magnetic field inside it is uniform and directed axially.

For a solenoid coil of infinite length at a point on its axial line, the magnetic field

where, n is number of turns per unit length.

At the end of solenoid

At the end field is half of at the centre this is called end effect.

**Toroidal Solenoids**

For a toroid (i.e. a ring shaped closed solenoid) magnetic field at any point within the core of toroid