Hello Student,

Magnetism is a vast chapter and also a very important one, I will try to provide you with all the formulas I know :

1. Magnetic Length = 5/6*Geometrical length
2. M(magnetic moment) = m(pole strength)*2L(magnetic length)
3. Bar magnet in cut into n equal parts parallel to its length magnetic moment = M/n (M = magnetic moment of uncut magnet)
4. Bar magnet cut into n equal parts perpendicular to its length = M/n (same as parallel)
5. Bar magnet cut in n equal parts parallely and m equal parts perpendicularly M' = M/n*m
6. Resultant Magnetic moment due to combination of magnets with like poles together = {M1^2 + M2^2 + (2*M1M2cosx)}^1/2
7. Resultant Magnetic moment due to combination of magnets with unlike poles together = {M1²+ M2²-(2*M1M2cosx)}^1/2
8. Force experienced when a a pole of strength m is placed at a point in a magnetic field B experiences a force F = mB {North pole experiences force towards the field, reverse is true for south pole }
9. Magnetic field at a point due to isolated magnetic pole B = μ*m/4π(r^2)
10. Magnetic Flux φ = BAcosθ [ θ  is angle made by magnetic field with area, A= Area ]
11. Couple Acting on bar magnet C = MBsinθ [ θ  is angle between magnetic moment and magnetic field ]
12. Work Done in rotating a magnetic dipole in a magnetic field from angular position θ1 to θ2 , W = MB(cosθ1 - cosθ2)
13. If the magnet is released workdone converts to kinetic energy , MB(cosθ1 - cosθ2) = Iω²/2
14. Field of a bar magnet at any point B = (μ/4π )* M[3cos²θ +1]­­­^1/2/d³
15. Magnetic Field due to a straight wire B = μi(sinφ  + sinω)/4πd ( φ  and ω  are angles made by the line joining the ends of wire with the point where field is to be found out )
16. Magnetic field at the centre of a circular coil carrying current B = μ i N/2R (N = Number of loops , i = current magnitude )
17. Field at an axial point of a circular loop , B = μiR²/2(x²+R²)^3/2
18. For a long solenoid magnetic induction on the axis B = μni [n = no. of turns per unit length of solenoid]

Most of the formulas are here but some are not as they cannot be understood until you see the diagrams. Also please learn the concepts and then if you practice well you will remember these formulas, otherwise chances are you will forget.