MAGNETIC EFFECT OF CURRENT, CBSE CLASS XII, PHYSICS NOTES PART IV

 

CBSE CLASS XII, MAGNETIC EFFECT OF CURRENT, PHYSICS NOTES-(PART IV)

MAGNETIC EFFECT OF CURRENT


NCERT Class XII Physics Chapter 4th. Magnetic Effect of Current Notes

Study Material and Notes of Chapter 3 Magnetic Effect of current Class XII Physics

ACCORDING TO THE CBSE SYLLABUS 2025-26

AMPERE’S CIRCUITAL LAW

Just as Gauss’s law is an alternative form of Coulomb’s law in electrostatics, similarly, we have Ampere’s circuital law as an alternative form of Biot-Savart law in magnetostatics. Ampere’s circuital law gives a relationship between the line integral of a magnetic field B and the total current that produces this magnetic field.                                                                                                                       

Ampere’s circuital law states that the line integral of the magnetic field around any closed circuit is equal to μ0 (Permeability constant) times the total current I threading or passing through this closed circuit. 

Ampere’s circuital law states that if the magnetic field is directed along the tangent to every point on the perimeter L of a closed curve and its magnitude is constant along the curve, then


Where I is the net current enclosed by the closed circuit.  The closed curve is called an Amperean loop. Which is a geometrical entity and not a real wire loop.

PROOF FOR A STRAIGHT CURRENT CARRYING CONDUCTOR

Let us consider an infinitely long straight conductor carrying a current I. From Biot-Savart law, the magnitude of the magnetic field due to the current-carrying conductor at a point, distance r from it is given by


From the figure, the field is directed along the circumference of the circle of radius r with the wire as centre. The magnitude of the magnetic field is same for all points on the circle. To evaluate the line integral of the magnetic field alone the circle.

Let us consider that a small current element along the circle. At every point on the circle, both magnetic field and current element are tangential to the circle so that the angle between them is zero.

Hence, the line integral of the magnetic field along the circular path is



This proves Ampere’ s law. This law is valid for any assembly of current and for any arbitrary closed loop.

 







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