Class 12 Physics Chapter 4 – Moving Charges and Magnetism Revision Notes

CBSE Class 12 Physics Revision Notes Chapter 4 Moving Charges and Magnetism

Biot – Savart law: The magnitude of Magnetic Field  is proportional to the steady current I due to an element  at a point P and inversely proportional to the distance r from the current element is,

• Magnetic field due to long straight current carrying conductor:
• If conductor is infinitely long, 
• Right-hand rule is used to find the direction of magnetic field due to straight current carrying conductor.
• Force on a Straight Conductor: Force F on a straight conductor of length  and carrying a steady current I placed in a uniform external magnetic field B, 
• Lorentz Force: Force on a charge q moving with velocity v in the presence of magnetic and electric fields B and E.
• Magnetic Force: The magnetic force  is normal to  and work done by it, is zero.
• Cyclotron: A charge q executes a circular orbit in a plane normal with frequency called the cyclotron frequency given by, 
  This cyclotron frequency is independent of the particle’s speed and radius.
• Magnetic Field due to Circular current carrying Coil: Magnetic field due to circular coil of radius ‘a’ carrying a current I at an axial distance r from the centre-
  
  At the centre of the coil, 
• Ampere’s Circuital Law: For an open surface S bounded by a loop C, then the Ampere’s law states that  where I refers to the current passing through S.
• If B is directed along the tangent to every point on the perimeter, then  Where Ie is the net current enclosed by the closed circuit.
• Magnetic Field: Magnetic field at a distance R from a long, straight wire carrying a current I is given by, 
  The field lines are circles concentric with the wire.
• Magnetic field B inside a long Solenoid carrying a current I:  Where n is the number of turns per unit length.
• For a toroid,  Where N is the total numbers of turns and r is the average radius.
• Magnetic Moment of a Planar Loop: Magnetic moment m of a planar loop carrying a current I, having N closely wound turns, and an area A, is 
• Direction of  is given by the Right – Hand Thumb Rule: Curl and palm of your right hand along the loop with the fingers pointing in the direction of the current, the thumb sticking out gives the direction of
• Loop placed in a Uniform Magnetic Field:

1. When this loop is placed in a uniform magnetic field B, Then, the force F on it is, F = 0
   And the torque on it is 
   In a moving coil galvanometer, this torque is balanced by a counter torque due to a spring, yielding.
    Where  is the equilibrium deflection and k is the torsion constant of the spring.

• Magnetic Moment in an Electron: An electron moving around the central nucleus has a magnetic moment , given by
   Where  is the magnitude of the angular momentum of circulating electron about the central nucleus.
• Bohr Magneton: The smallest value of  is called the Bohr magneton μBOr