- The Earth has a magnetic field generated by circulating electric currents in its molten metallic core. - A compass needle aligns with the Earth's magnetic field, pointing north. However, the North Magnetic Pole is actually the south magnetic pole. - All matter is magnetic to some degree due to the orbital and spin motions of electrons. Materials can be classified as diamagnetic, paramagnetic, or ferromagnetic based on their response to magnetic fields.

2. A magnetic Compass
•The Earth itself is a giant magnet.
• The planet gets its magnetic field from
circulating electric currents within the
molten metallic core.
•A compass points north because the
small magnetic needle in it is suspended
so that it can spin freely inside its casing
to align itself with the planet's magnetic
field.
• Paradoxically, what we call the Magnetic
North Pole is actually a south magnetic
pole because it attracts the north
magnetic poles of compass needles.
Magnetic Field

3. •The origin of magnetism lies in the orbital and spin motions of electrons and
how the electrons interact with one another.
•The best way to introduce the different types of magnetism is to describe how
materials respond to magnetic fields.
•This may be surprising to some, but all matter is magnetic. It's just that some
materials are much more magnetic than others.
•The magnetic behavior of materials can be classified into the following three
major groups:
1. Diamagnetism
2. Paramagnetism
3. Ferromagnetism
Diamagnetic materials
Diamagnetism is a fundamental property of all matter, although it is usually
very weak. It is due to the non-cooperative behavior of orbiting electrons when
exposed to an applied magnetic field. Diamagnetic substances are composed
of atoms which have no net magnetic moments (ie., all the orbital shells are
filled and there are no unpaired electrons). However, when exposed to a field,
a negative magnetization is produced and thus the susceptibility is negative.

4. •magnetic susceptibility χ is a measure of how much a material will become
magnetized in an applied magnetic field.
• Mathematically, it is the ratio of magnetization M (magnetic moment per unit
volume) to the applied magnetizing field intensity H.
• This allows a simple classification of most materials' response to an applied
magnetic field into two categories:
• an alignment with the magnetic field, χ > 0, called paramagnetism
•or an alignment against the field, χ < 0, called diamagnetism.
•Paramagnetic materials
•This class of materials, some of the atoms or ions in the material have a net
magnetic moment due to unpaired electrons in partially filled orbitals.
•One of the most important atoms with unpaired electrons is iron.
•However, the individual magnetic moments do not interact magnetically.
•like diamagnetism, the magnetization is zero when the field is removed.
•In the presence of a field, there is now a partial alignment of the atomic
magnetic moments in the direction of the field, resulting in a net positive
magnetization and positive susceptibility.

5. Ferromagnetic materials
•the atomic moments in these materials exhibit very strong interactions.
•These interactions are produced by electronic exchange forces and result in a
parallel or antiparallel alignment of atomic moments.
• Exchange forces are very large, equivalent to a field on the order of 1000
Tesla, or approximately a 100 million times the strength of the earth's field.
•The exchange force is a quantum mechanical phenomenon due to the
relative orientation of the spins of two electron.
•Ferromagnetic materials exhibit parallel alignment of moments resulting in
large net magnetization even in the absence of a magnetic field.

7. •field of electromagnetic energy that transfers the forces of a magnet.
•often depicted with field lines. It is also possible to make it visible with iron
filings on a sheet of paper with a magnet underneath.
•Symbol B and Units Tesla(SI) and Gauss(CGS) 1 Tesla= 104 Gauss
The properties of magnetic field lines can be summarized by these rules:
•The direction of the magnetic field is tangent to the field line at any point in space.
•A small compass will point in the direction of the field line.
•The strength of the field is proportional to the closeness of the lines. It is exactly
proportional to the number of lines per unit area perpendicular to the lines (called the
areal density).
•Magnetic field lines can never cross, meaning that the field is unique at any point in
space.
•Magnetic field lines are continuous, forming closed loops without beginning or end.
They go from the north pole to the south pole.
Magnetic field

8. •The magnetic flux density B describes the density and direction of
the field lines that run through an area A.
•The denser the field lines, the larger the magnetic flux density.
The magnetic flux Φ is the magnetic flux density which runs
through an imagined area.
•If the field lines run in a straight line (e.g. between the poles of a
horseshoe magnet), the magnetic flux Φ through a certain area A
which runs vertically to the flux can be calculated as follows:
•Φ(weber) = B•A
Magnetic flux

9. Snow rule: Around a South pole field lines
are clockwise and vice versa
Right hand thumb rule and Cork
Screw Rule

10. Magnetic field of a bar magnet(natural magnet) and a
solenoid (artificial magnet)is quite similar
•The applications of (artificial magnets)electromagnets are nearly countless.
• Faraday’s Law of Induction forms the basis for many aspects of our modern
society including not only electric motors and generators, but electromagnets
of all sizes.
•The same principle used by a giant crane to lift junk cars at a scrap yard is also
used to align microscopic magnetic particles on a computer hard disk drive to
store binary data, and new applications are being developed every day.

11. Electromagnetic Induction or Induction is a process in which a conductor (coil
as shown in the diagram) is put in a particular position and magnetic field
keeps varying or magnetic field is stationary and a conductor is moving. This
produces a Voltage or EMF (Electromotive Force detected by a Galvanometer)
across the electrical conductor.

12. Faraday’s Laws
•Electrons are teeny tiny magnets.
•They have a north and a south pole, too, and spin around an axis.
•This spinning results in a very tiny but extremely significant magnetic field.
• Every electron has one of two possible orientations for its axis.
•In most materials, atoms are arranged in such a way that the magnetic
orientation of one electron cancels out the orientation of another.
•Iron and other ferromagnetic substances, though, are different.
• Their atomic makeup is such that smaller groups of atoms band together into
areas called domains, in which all the electrons have the same magnetic
orientation as shown in the diagram

14. Electromagnetic Induction

15. Lorentz force
– The combination of electric and magnetic forces on a moving charge
q is known as the Lorentz force.
– F = q(E + v × B)
– Where magnetic Lorentz force is given by: FB = qv × B
where charge q is moving with velocity v in the presence of
magnetic field B
– Suppose a conductor of length L carries current I. As it is carrying
current (DC), some flux lines will be generated around the conductor
– This current carrying conductor is placed between two poles of a
horse shoe magnet of flux density B . This magnet is tightly fixed to
the ground. Conductor is not fixed, rather it is free to move.

16. Force on a current carrying conductor
•A conductor consists of large no. of free electrons.
• Current on the conductor means drifting of such a free electron in any fixed direction
•Consider a conductor having length L, cross-section area A in a uniform magnetic field.
• If n be the number of electrons per unit volume (electron density), vd be the drift
velocity of electron having electronic charge e then the current on the conductor is

17. – Due to the motion of electron in magnetic field B, each electron experience
Lorentz’s magnetic force.
Total number of charges on the conductor is
– Total force experienced by the conductor is

18. •F=BILsinθ, gives the magnitude of this force
•θ is angle that conductor makes with the magnetic field.
•The direction of this force is always right angles to the plane containing both
the conductor and the magnetic field, and is predicted by Fleming’s Left-
Hand Rule:
• A left hand can be held, as shown in the illustration, so as to represent
three mutually orthogonal axes on the thumb, fore finger and middle finger.
Each finger is then assigned to a quantity (mechanical force F, magnetic field
B and electric current I. The right and left hand are used for generators and
motors respectively.
•Fleming's right-hand rule shows the direction of induced current when a
conductor attached to a circuit moves in a magnetic field. It can be used to
determine the direction of current in a generator's windings.

20. Principle
Torque acts on a current carrying coil suspended in the uniform magnetic
field. Due to this, the coil rotates. Hence, the deflection in the coil of a
moving coil galvanometer is directly proportional to the current flowing in the
coil.
Construction
It consists of a rectangular coil of a large number of turns of thinly insulated
copper wire wound over a light metallic frame. The coil is suspended
between the pole pieces of a horseshoe magnet by a fine phosphor – bronze
strip from a movable torsion head. The lower end of the coil is connected to a
hairspring of phosphor bronze having only a few turns.

21. The other end of the spring is connected to a binding screw. A soft iron cylinder is
placed symmetrically inside the coil. The hemispherical magnetic poles produce a
radial magnetic field in which the plane of the coil is parallel to the magnetic field in all
its positions. A small plane mirror attached to the suspension wire is used along with a
lamp and scale arrangement to measure the deflection of the coil.
Moving coil Galvanometer
– Working
– Let PQRS be a single turn of the coil. A current I flows through the coil. In a
radial magnetic field, the plane of the coil is always parallel to the magnetic
field. Hence the sides QR and SP are always parallel to the field. So, they do
not experience any force. The sides PQ and RS are always perpendicular to
the field.
– PQ = RS = l, length of the coil and PS = QR = b, breadth of the coil. Force on
PQ, F = BI (PQ) = BIl. According to Fleming’s left-hand rule, this force is
normal to the plane of the coil and acts outwards.

22. These two equal, oppositely directed parallel forces having different lines of
action constitute a couple and deflect the coil. If there are n turns in the
coil, the moment of the deflecting couple = n Bil b
Hence the moment of the deflecting couple = nBIA
When the coil deflects, the suspension wire is twisted. On account of
elasticity, a restoring couple is set up in the wire. This couple is proportional
to the twist. If θ is the angular twist, then, the moment of the restoring
couple = kθ, where k is the spring constant.
At equilibrium, deflecting couple = restoring couple so: nBIA = kθ
Hence we can write, nBIA = kθ
I = (k / nBA) × θ where G= k / nBA is the Galvanometer constant.
Hence I α θ
The deflection θ is indicated on the scale by a pointer attached to the
spring.

23. Conversion of Galvanometer into Ammeter
A galvanometer having resistance Rg
is converted into an ammeter by connecting a low resistance in parallel with the
galvanometer. This low resistance is called shunt resistance S. The scale is now
calibrated in ampere and the range of ammeter depends on the values of the shunt
resistance.

24. Conversion of Galvanometer into
Voltmeter
– A galvanometer can be converted in to a voltmeter by connecting a high
resistance in series with it.
– The scale is calibrated in volt.
– The value of the resistance connected in series decides the range of the voltmeter.
– Galvanometer resistance =G
– The current required to produce full scale Deflection in the galvanometer =Ig
– Range of voltmeter =V
– Resistance of voltmeter =R
– Since R is connected in series with the galvanometer, the current through the
galvanometer,
Ig​=R+GV
– ∴R=IgV​−G