Download 7TH CLASSES PHYSICS DAILY PLAN

10TH CLASSES
PHYSICS
DAILY PLAN
SUBJECT: M
MA
AG
GN
NEETTIISSM
M
AIM:To learn the properties of the magnets
DURATION: 120 min
REAL LIFE:Magnets
PRESENTATION:
M
Maaggnneettiicc pprrooppeerrttiieess::
A magnet is an object that has the property of attracting
magnetic substance.
Substances, which are attracted by a magnet, are called
magnetic, and those, which are not attracted by a magnet, are
called nonmagnetic.
For ex: Iron, Cobalt, Nickel are magnetic but Aluminum is a
nonmagnetic material. (SHOW!).
If you have a magnetic material you can create an
artificial magnet by rubbing it with another magnet.(SHOW!).
In nature a magnet is an iron oxide (magnetite) but we can
produce artificial magnets in different sizes and shapes, such
as bar magnet, U shaped magnet horse-shoe magnet round
magnet, etc…FIGURES
M
Maaggnneettiicc ppoolleess::
If a bar magnet is dipped into iron filings, it holds filings in
large amount near its two ends (SHOW)
This shows that, the forces, which make the fillings collect,
are concentrated mainly near the ends. These two ends are
called poles of magnet. Poles are always found in pairs. In
another words a magnet has two poles (north and south) and
there is no magnet having only one pole. Two poles have
exactly the same strength of attraction.
field lines and the force acting S pole is in the opposite
direction of the field lines.
M
Maaggnneettiicc FFiieelldd,, FFiieelldd IInntteennssiittyy,, FFiieelldd LLiinneess
When iron filings are scattered on a sheet of plastic above a
bar magnet become aligned in certain directions. The lines
around the magnet are called magnetic field lines. The number
of magnetic field lines passing through a unit surface is called
magnetic field strength or magnetic flux density or magnetic
inductor.
N
N
S
S
N
S
N
N
3) Magnetic Field Vector (B):
 B vector is always tangent to field lines.
 Magnitude of the vector at a point shows strength of field.
B
B
Bar magnet
When a bar magnet is suspended or pivoted so that it can turn
freely about a vertical axis in a horizontal plane, it turns and
omes to rest approximately north- south direction.
For this reason, the end of magnet that points north is called
its north pole (N), and the other end is called its south pole
(S).
N
S
Bar magnet
N
S
N
S
N
S
B
B
Therefore: If field line is circular, B
vector is perpendicular to radius.
Unit: Unit of B is Tesla (T), or
Weber
m
2
(Wb/m2)
Wb
(SI system)
m2
Method of Producing Magnets
We can make artificial magnets since natural ones are not easy
to find.
to do this, we stroke one pole of a bar
a) by stroking:
magnet along in a iron bar several
times in the same direction then, iron
Ñ
bar becomes magnet.
1T=1
N
S
N
S
U magnet
Like poles (N-N), (S-S) repel each other and opposite poles
attract each other.

A compass needle is also a bar magnet and shows (NS) directions.
M
Maaggnneettiicc FFiieelldd:: ((BB))
If a bar magnet is brought near another magnet, they apply a
force on one another. The region about a magnet where its
influence is understood or shown is called ``magnetic field of
that magnet``.
 Magnetic field lines are directed away from on N pole
and towards on S pole.
 Where the magnetic field lines are close together the field
is strong and where they separated, the field is weak.
At the two poles, field is the strongest.
 When you change the location of a test compass around a
bar magnet, at any point needle of compass will show a
particular direction and these shows magnetic field
around a magnet is variable and has a direction.

If a compass needle is located in a uniform magnetic
field, the force acting N-pole is in the direction of magnetic
b) by contact:
If either N or S pole of a magnet
comes into contact with an iron
nail then, nail becomes magnet.
N
S
c) by induction:
N
S
If iron nail is brought near to a
magnet, because the magnetic
field of an iron bar affect the
nails, nail becomes a magnet for
a while and can attract iron
filings.
. . Iron filings
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d) By the means of earth’s magnetic field
If you place an iron bar at an angle with the horizontal and
strike bar with a hammer several times. Then the iron bar
becomes a magnet. Because, sudden motions of the
domains in the iron bar are aligned in the direction in the
earth’s magnetic field
PPrroodduucciinngg EElleeccttrroo m
maaggnneett
By using electric current we will produce some effect of a
magnet.
When electric current passes through a
conducting wire produces circular magnetic
field lines around the conductor. When you
pass this electric current through a coil, an
intense magnetic field is formed. And when
you enter an iron bar into the coil, the bar
becomes electromagnet.
1.Diamagnetics: if Mr less than unity (meanly Mr=0,999982)
(for lead). They make the field a little weaker.
2.Paramagnetics: If Mr is slightly greater than unity
(1,000022) for Aluminum. They make the field a little
stronger.
3.Ferromagnetic materials: If Mr>>1 much larger than unity
(100,1000,…)(iron, cobalt, nickel). They make the field much
stronger.
The Magnetic Field of the Earth
N
The earth is a giant magnet
itself. The geographical pole
and magnetic pole are not at
the same place.
2100 km
S
N
M
Maaggnneettiicc FFlluuxx ((O
O))
Magnetic flux is the total number of magnetic field lines
passing thruogh a certain cross-sectional area.
S
Declination angle is between
geographical and magnetic
north.
Inclination angle is between
the magnet needle and
horizontal.
[Inclination angle is zero only at the magnetic equator]
  B A
Magnetic filed of earth is about 10-5 T.
B

if the chosen surface is not perpendicular to the line then:
N
We define normal to the surface
α
O=BAcos α
α is the angle between normal to
the surface and the magnetic field
lines.
ex1:
The uniform magnetic field in a certain region has a
magnitude of 2T, and its direction is horizontal. The plane of a
rectangular coil 20cm by 30cm makes an angle of 37 0 with the
field.
Compute the flux, O, through the coil.
Solution: A=20.30=6.10-2.m2
O=BA.cos α=6.10-2.2cos 530
O= 0,072 wb
Magnetic Permeability (μ)
It is a characteristic property of a substances and a measure of
ability to increase or decrease the value of B in the region.
Suppose that the uniform magnetic field at a certain point in
vacuum is Bo. if a piece of iron is placed in the region, the
field at that point will change to a new value B.
The relative permeability μb of the material is given as
μb=magnetic field in material / magnetic field in vacuum in
symbols, μb=B/Bo
We can also write the formula between permeability’s as
follows μb= μ / μo =oermeability of material/permeability of
vacuum.For vacuum, permeability μo =4П.10-4wb/AM
Relative permeable of vacuum is 1. (and also air)
Shortly, magnetic permeability of a substance is the
ability to increase or decrease the value of B in the region.
HOMEWORK:
MULTIMEDIA: electromagnetism, akademedia
DEMONSTRATION: magnets, field lines
EXPERIMENT:
TEACHER:
DIRECTOR:
We can classify substances into three groups according to
their relative magnetic permeabilities.
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