**MAGNETIC CIRCUIT** :- Magnetic flux in a closed loop or mesh is defined as the **MAGNETIC CIRCUIT. **

**SOME TERMS USED IN MAGNETIC CIRCUITS ARE : **

**1.MAGNETIC FLUX** :- Number of magnetic lines of force produced by a magnet is called **Magnetic flux.**It is denoted by ϕ.

2.**MAGNETIC FIELD** :- It is the region around the magnet where poles exhibit force of attraction or force of repulsion.

3.**MAGNETIC FLUX DENSITY **:- Magnetic lines of force per unit area at right angles to the flux. It is denoted by **B.** Its unit is **TESLA.B = ϕ/A** where **ϕ** denotes magnetic flux and A denotes area .

4.**MAGNETIC INTENSITY OR MAGNETISING FORCE :-** The force acting on a unit N-pole placed at a point in the magnetic field is called **MAGNETIC FIELD INTENSITY** at that point . It is denoted by **H.**

**H = ℑ / l.**

**Where**

** ℑ =applied MMF in ampere-turns**

** l =average length of the magnetic path in mete**r.

5. **PERMEABILITY :-** The ability of a magnetic material to allow magnetic lines of force to pass through it is known as **MAGNETIC PERMEABILITY.** It is denoted by (μ).

6. **RELATIVE PERMEABILITY :-** It is the ratio of permeability of material to the permeability of air . It is denoted by μ_{r}.

where μ_{r} = μ / μ_{0}.

7. **INTENSITY OF MAGNETISATION :-** The pole strength developed per unit area of the bar is called **INTENSITY OF MAGNETISATION.** It is denoted by **J.**

8. **MAGNETO MOTIVE FORCE :-** It is the work done in moving a unit magnetic pole around the magnetic circuit is called **MAGNETO MOTIVE FORCE (M.M.F)**.

**M.M.F = NI Amphere turns**.

**where N = no of turns. and I = current . **

9. **RELUCTANCE :-** It is the resistance offered to the magnetic flux by a magnetic circuit is called **RELUCTANCE.** It is denoted by **S.**

**S = l / μ A** .