Two bodies even after being neutral (showing no electric interaction) may attract / repel strongly
if they have a special property. This property is known as magnetism. The force with which they
attract or repel is called magnetic force. Those bodies are called magnets. Later on we will see
that it is due to circulating currents inside the atoms. Magnets are found in different shape but for
many experimental purposes, a bar magnet is frequently used. When a bar magnet is suspended
at its middle, as shown, and it is free to rotate in the horizontal plane it always comes to
equilibrium in a fixed direction.
Pole strength magnetic dipole and magnetic dipole moment
Magnetic field and strength of magnetic field.
Magnet in an external uniform magnetic field
MAGNETIC EFFECTS OF CURRENT
(AND MOVING CHARGE)
The motion of anything is a relative term. A charge may appear at rest by an observer (say O1) and
moving at same velocity 1 v ï² with respect to observer O2 and at velocity 2 v ï² with respect to
A charge particle ‘q’ has velocity v as shown in the figure. It is at
Biot-savart’s law (B
due to a wire)
(Derivation can be seen in a standard text book like your school
book or concept of physics of HCV part-II)
The direction of the magnetic field at a point P due to a
straight wire can be found by a slight variation in the righthand
thumb rule. If we stretch the thumb of the right hand
along the current and curl our fingers to pass through the
point P, the direction of the fingers at P gives the direction
of the magnetic field there.
If the wire is infinitely long then the magnetic field at ‘P’ (as
Direction of B
: The direction of the magnetic field at the
centre of a circular wire can be obtained using the right-hand thumb
rule. If the fingers are curled along the current, the stretched thumb
will point towards the magnetic field
(figure).
B
B
Direction can be obtained by right hand thumb rule. curl your fingers in the direction of the
current then the direction of the thumb points in the direction of B
at the points on the
axis.
The pattern of the magnetic field is comparable with the magnetic field produced by a bar magnet
Solenoid contains large number of circular loops wrapped around a non-conducting cylinder. (it may
be a hollow cylinder or it may be a solid cylinder
AMPEREs circuital law
To find out magnetic field due to infinite current carrying wire
is uniformly distributed on the whole circumference
Solid infinite current carrying cylinder
