TEMA PARA LA MATERIA DE QUÍMICA...t/t

1. QBA Miguel A. Castro Ramírez

2. Magnetic Fields
 The region where the magnetic forces act is
called the “magnetic field”

3. EARTH’S
MAGNETISM
The Earth itself has a huge
magnetic field - as if it had a
huge bar magnet embedded
at its centre. The Earth’s
magnetic field lines emerge
from near the geographical
north pole and re-enter it at
the south pole. The nature of
the field around the Earth
varies in both strength and
direction. The Earth’s
magnetic field is strongest at
the magnetic poles and
weakest near the Equator.

4. Why does the Earth have a magnetic field?
The Earth has, at its centre, a
dense liquid core, of about
half the radius of the Earth,
with a solid inner core. This
core is though to be mostly
made of molten iron and
nickel perhaps mixed with
some lighter elements.
Circulating ions of iron and
nickel in highly conducting
liquid region of earth’s core
might be forming current
loops and producing earth’s
magnetism.

5. The Earth’s magnetic field

6. Magnetic
eleMents
 Magnetic Declination
 Magnetic Inclination or Magnetic Dip

7. Magnetic Declination
The small angle
between magnetic
axis and
geographic axis at
a place is defined
as the magnetic
declination.

8. Magnetic Inclination or
Magnetic Dip
The angle which
the direction of
total strength of
earth’s magnetic
field makes with
a horizontal line
in magnetic
meridian.

9.  Atoms themselves have magnetic properties
due to the spin of the atom’s electrons.
 Groups of atoms join so that their
magnetic fields are all going in the same
direction
 These areas of atoms are called “domains”

10. When an unmagnetized substance is placed in a magnetic
field, the substance can become magnetized.
This happens when the spinning electrons line up in the
same direction.

11.  The metals affected by
magnetism consist of tiny
regions called 'Domains'
which behave like tiny
magnets. Normally they are
arranged in the magnetic
material all pointing in
different directions in a
completely random fashion
and so their magnetic effects
cancel each other out. If an
object is magnetized it is
because the domains are all
made to point in the same
direction. This can be done by
stroking the magnetic
material with a magnet (or
magnets) as shown in the
diagram. When aligned the
domains reinforce one
another and create north and
south poles at either end.

12. Classification of magnetic
materials
 Diamagnetic Substances
 Paramagnetic substances
 Ferromagnetic substances

13. Diamagnetic substances
• The diamagnetic substances are those in
which the individual atoms or ions do not
possess any net magnetic moment on
their own.
• When such substances are placed in an
external magnetizing field, they get feebly
magnetized in a direction opposite to a
magnetizing field.

14. Paramagnetic Substances
 Paramagnetic substances are those in
which each individual atom or molecule or
ion has a net non zero magnetic moment
of its own.
 When such substances are placed in an
external magnetic field, they get feebly
magnetized in the direction of the
magnetizing field.

15. Ferromagnetic materials
Ferromagnetic
Domains in
Materials Ferromagnetic
material are those
in which each
individual atom or
molecule has a
non zero magnetic
moment

16. Hysteresis Curve
 The relationship between magnetic field
strength (H) and magnetic flux density (B) will
follow a curve up to a point where further
increases in magnetic field strength will result
in no further change in flux density. This
condition is called magnetic saturation till
point (a)

17. • the plotted relationship will follow a
different curve back towards zero field
strength at which point it will be offset from
the original curve by an amount called the
remanent flux density or Retentity as
shown in graph at point (b)
• The 'thickness' of the middle, describes
the amount of hysteresis, related to the
coercivity of the material as from (c) to (f)

21. Hysteresis curve of soft and steel
 The retentivity of soft
iron > retentivity of steel
 Soft iron is more strongly
magnetized than steel
 Coercivity of soft iron <
Coercivity of steel
 Hence, soft iron loses its
magnetism more rapidly
than steel does.

22. An
electromagnet
 A soft iron rod has no
magnetic field
 When current flows in
the wire the soft iron
becomes magnetized so
a magnetic field is
detected by the plotting
compasses.

23. THANK YOU
Efforts By :-
Lovish Uppal
Rajat Verma