MAGNETISM
Unit - 9
MAGNETIC FIELDS
A magnet will attract something that comes in contact
with its magnetic field.
Definition - The magnetic field is the area around a
magnet in which the effect of magnetism is felt.
Magnetic field can be detected in two ways 1. See weather magnetic object moves because of
attraction
2. Use a compass
Magnetic field lines
Rules of magnetic field lines ●
●
●
●
●
Join opposite poles
Have arrows that point N to S
Must not touch each other
Must not cross each other
Like poles repel and unlike
poles attract each other
TRY DRAWING THE MAGNETIC FIELD LINES FOR THESE MAGNETS -
A. HORSE SHOE MAGNET
B. RING MAGNET
C. SPHERICAL MAGNET
In a strong magnet
● All the lines are
closer together
● The field will extend
further away from
the magnet
TEXTBOOK QUESTIONS pg 296
Story of Magnes
According to Greek legend,
magnetism was first discovered by
a shepherd named Magnes, who
lived in Magnesia, Greece.
Magnes was herding his sheep
through the mountains. Suddenly
he noticed the iron nails in his
shoes got stuck to a rock. The iron
in his stick and nails had become
attracted to the magnetic rock. The
stone was named magnetite, after
the name of the shepherd or the
country it was found in. It was also
known as a loadstone because of
its attractive properties.
COMPASS AND THE EARTH’S MAGNETIC FIELD
LINK https://www.youtube.com
/watch?v=Eup2J0oAq9Y
Earth’s magnetic field
Earth’s magnetic field is also referred
to as the geomagnetic field.
The Earth’s magnetic field extends far
and wide but is very weak in terms of
field strength
There is one theory that explains how
the earth’s magnetism is caused:
Dynamo effect: The earth gets its
own magnetic field lines because of
the presence of the metallic fluids that
are present at the outer core as well
as in the inner core. The outer core
consists of molten iron, while the inner
core has the solidified elements.
The north end of a
magnet in a
compass is
attracted to the
south magnetic
pole, which lies
close to the
geographic north
pole. Magnetic field
lines outside of a
permanent magnet
always run from
the north magnetic
pole to the south
magnetic pole
NORTHERN LINES
Earth's magnetic field steers the charged
particles towards the poles. The shape of
Earth's magnetic field creates two auroral
ovals above the North and South Magnetic
Poles. That is why auroras occur almost
every night in the northern sky, from
August to May.
LINK https://www.youtube.com/watch?v=HJfy8acFaOg
TEXTBOOK QUESTIONS PG - 303
Properties of Magnet
A few properties of the magnet are as follows:
Attractive Property – Materials like iron, nickel and
cobalt are attracted by magnets
Repulsive Property – Like poles repel each other
while unlike poles attract each other
Directive Property – A freely suspended magnet
always points in the north-south direction.
ELECTROMAGNETS
●
●
●
An electromagnet can be defined as a magnet which
functions on electricity.
Unlike a permanent magnet, the strength of an
electromagnet can be changed by changing the amount
of electric current that flows through it.
If the current flow is cut, the property of magnetism
ceases to exist.
MAKING 1. An electromagnet is made by wrapping a wire around
an magnetic material. The wire is wrapped around in a
coil and the middle part of the coil is called as the core.
2. When current is passed through the magnetic material
become magnetised.
3. When current is off the magnetic material loses most of
its magnetism.
LINK - https://www.youtube.com/watch?v=cxELqN7wjS0
Uses Of Electromagnet
Home Appliances - Some electromagnet uses in the home
include an electric fan, electric doorbell, induction cooker,
magnetic locks, etc.
Medical Field - MRI scan which is short for Magnetic
Resonance Imaging is a device that uses electromagnets. The
device can scan all the tiny details in the human body with the
help of electromagnetism.
Communication Devices and Power Circuits - The
electromagnetic pulses and the interaction of the signals make
mobiles and telephones very handy.
Sorting scrap metal
TEXTBOOK QUESTIONS pg 309
STRENGTH OF ELECTROMAGNETS
TEXTBOOK QUESTIONS pg - 313
CHECK YOUR PROGRESS
THANK YOU
"The mind is not a vessel to be filled but a fire to be ignited." –
Plutarch