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
