Introduction to Magnetostatics

1. MAGNETOSTATICS
INTRODUCTION TO
KRISHNA SREE R S
ASSISTANT PROFESSOR
DEPT OF PHYSICS
SNCW,KOLLAM

2.  Magnetostatics is the study of magnetic fields in systems where the currents are steady (not
changing with time). It is the magnetic analogue of electrostatics, where the charges are
stationary.
 Current , I :An electric current is the rate of flow of electric charge.SI unit is ampere(A).It is
a scalar quantity
I =
𝑄
𝑡
; Q is the charge flowing in time t
One Ampere of current is equal to one coulomb of charge flowing through a surface
in one second
Current Density , J : Current flowing per unit area perpendicular to the direction of flow .
J is a vector quantity . SI unit is A/m2

3. * Find out the differences and relation between current & current density

4.  Magnetic field ,B : Space surrounding a magnet where magnetic force is
experienced.It can be represented by lines of force.SI unit is weber/m2
or Tesla (T)

5.  Magnetic Flux, ɸ : The number of lines of force passing normally through
a given area .SI unit is weber(Wb)
 Magnetic Flux density , B :Magnetic flux per unit area.( or strength of
magnetic field)
B =
ɸ
𝐴
SI unit is Wb/m2 or Tesla(T)

6. OERSTED’S EXPERIMENT
 Oersted performed an important experiment which showed that there was a
connection between electricity and magnetism. When a current was switched on
through a wire, it made a compass needle turn so that it was at right angles to the wire.
The current had produced a magnetic field strong enough to cause the compass needle
to turn.

7.  To find the direction of magnetic field
 (i) Maxwell’s Cork Screw rule : Suppose a screw is placed in the direction of
conductor current flow. Now the screw is rotated in such a manner that it
moves in the direction of the current flow, then direction of magnetic field is
in the same direction of rotation of the screw.

8.  (ii) The right hand grip rule :Suppose that the current carrying conductor is
held in the right hand and the fingers are wrapped around the conductor and
the thumb is stretched in the direction of current flow (as shown below in the
figure). Then wrapped fingers will give the direction of circular magnetic field
lines.

9. BIOT-SAVART LAW
 Biot-Savart’s law is an equation that gives the magnetic field produced due to
a current carrying element.
This is an inverse square law(magnetic field is inversely proportional to square of
the distance r of point p

10.  Case 1 , when θ = 0 ,dB=0 (dl & r are parallel)
 Case 2 , when θ =90 , sin θ =1 ,dB= 𝑚𝑎𝑥 (magnetic field is maximum in a
plane perpendicular to the current element)

11. THANK YOU