Electric Current and Magnetism The Nature of Magnetism: Electricity’s Silent Partner Magnetism is a property of a material that enables to attract or repel other materials. The presence and strength of the material’s magnetic properties can be observed by the effect of the forces of attraction and repulsion on other materials. What makes magnets? Magnets are actually created by tiny spinning electrons in an atom. The electrons move about the nucleus and spin like a top, creating a tiny magnetic field. If electrons are spinning in the same direction there is more magnetism, while electrons spinning in opposite directions cancel out each others’ magnetic fields. Magnetic fields are invisible, we can only see the effects of the magnetic force.  Magnetic Field: The space around a magnet in which a magnetic force is exerted — The shape of a magnetic field is revealed by magnetic field lines  Directed away from north poles and toward south poles Magnets have two ends or poles, called north and south poles. At the poles of a magnet, the magnetic field lines are closer together. The magnetic field lines around horse-shoe and disk magnets are closest together at the magnets’ poles. Unlike poles of magnets attract each other and like poles of magnets repel. Magnetic Poles: A region on a magnet which produces magnetic forces  The poles of a suspended magnet will align themselves to the poles of the Earth  Fundamental Rule: Like poles repel; opposite poles attract  If a force of attraction only is possible between an object and a magnet, then the object interacting with the magnet contains a ferromagnetic substance and is considered naturally magnetic.  If a force of repulsion is only between an object and a magnet, then the object interacting with the magnet may also be a permanent magnet or a temporarily magnetized ferromagnetic material.  Materials which are attracted by a magnet are known as magnetic materials. Iron, cobalt, nickel and many alloys of these metals like steel and alnico are magnetic.  Magnetic materials can be used to make permanent or temporary magnets unlike the non-magnetic materials which cannot. INDUCED MAGNETISM The process by which the screws become magnets is called Electric/Magnetic Induction. This same process is the reason why magnets attract non-magnetized magnetic substances such as the screw. The screw becomes an induced magnet with the end nearer the magnet having an opposite polarity to that of the permanent magnet. Hence attraction happens after magnetic induction occurs. The quicker way to know the polarity of a permanent or induced magnet is by the use of a magnetic compass. Compass needle is a small magnet that is free to pivot in a horizontal plane about an axis and that the end of the magnet that points to geographic north is called the north (N) pole. Likewise, the opposite end of the magnet is the south (S) pole.What are magnetic domains? Magnetic substances like iron, cobalt and nickel

1. Electric Current and Magnetism
The Nature of Magnetism: Electricity’s Silent Partner
Magnetism is a property of a material that enables to attract or repel other materials. The presence
and strength of the material’s magnetic properties can be observed by the effect of the forces of
attraction and repulsion on other materials.
What makes magnets?
Magnets are actually created by tiny spinning electrons in an atom. The electrons move about the
nucleus and spin like a top, creating a tiny magnetic field.
If electrons are spinning in the same direction there is more magnetism, while electrons spinning in
opposite directions cancel out each others’ magnetic fields. Magnetic fields are invisible, we can only
see the effects of the magnetic force.
 Magnetic Field: The space around a magnet in which a magnetic force is exerted
— The shape of a magnetic field is revealed by magnetic field lines
 Directed away from north poles and toward south poles
Magnets have two ends or poles, called north and south poles. At the poles of a magnet, the
magnetic field lines are closer together.
The magnetic field lines around horse-shoe and disk magnets are closest
together at the magnets’ poles.
Unlike poles of magnets attract
each other and like poles of magnets
repel.

2.  Magnetic Poles: A region on a magnet which produces magnetic forces
 The poles of a suspended magnet will align themselves to the poles of the Earth
 Fundamental Rule: Like poles repel; opposite poles attract
 If a force of attraction only is possible between an object and a magnet, then the object interacting
with the magnet contains a ferromagnetic substance and is considered naturally magnetic.
 If a force of repulsion is only between an object and a magnet, then the object interacting with the
magnet may also be a permanent magnet or a temporarily magnetized ferromagnetic material.
 Materials which are attracted by a magnet are known as magnetic materials. Iron, cobalt, nickel
and many alloys of these metals like steel and alnico are magnetic.
 Magnetic materials can be used to make permanent or temporary magnets unlike the non-
magnetic materials which cannot.
INDUCED MAGNETISM
The process by which the screws become magnets is called Electric/Magnetic Induction. This
same process is the reason why magnets attract non-magnetized magnetic substances such as the
screw. The screw becomes an induced magnet with the end nearer the magnet having an opposite
polarity to that of the permanent magnet. Hence attraction happens after magnetic induction occurs.
v
A permanent magnet can induce temporary magnetism in a ‘soft’ magnetic material.
•This causes attraction, but cannot cause repulsion.
•Use repulsion to test if an object is already magnetized.
The quicker way to know the polarity of a permanent or induced magnet is by the use of a magnetic
compass. Compass needle is a small magnet that is free to pivot in a horizontal plane about an axis
and that the end of the magnet that points to geographic north is called the north (N) pole. Likewise,
the opposite end of the magnet is the south (S) pole.
What are magnetic domains?
Magnetic substances like iron, cobalt, and nickel are composed of small areas where the groups of
atoms are aligned like the poles of a magnet. These regions are called domains. All of the domains of
a magnetic substance tend to align themselves in the same direction when placed in a magnetic field.
These domains are typically composed of billions of atoms.
When these are placed within an external magnetic field, the weaker domains unify with the stronger
domains. These line up more uniformly inducing greater magnetic field strength. Materials made from
these elements and its alloys are classified as ferromagnetic and make strong permanent magnets.
Thus, magnets brought near materials that contain one of the ferromagnetic metals will induce

3. magnetism in the object and thus attract it. Magnetic induction also makes iron filings and compass
pointers align themselves along the magnetic field lines that caused induction.
MAGNETISING AND DEMAGNETISING
Make a magnet
• by stroking
• by using DC coil carrying current
• by tapping while aligned with the Earth’s field
Demagnetize a magnet
• by dropping or banging randomly
• by heating
• by applying a diminishing AC current
DEMAGNETIZED Microscopic structure
MAGNETIZED Electron spin, inside atoms,
is the main cause of
ferromagnetism.
In a material, clusters of atoms line up with each others’ magnetic field – just like a compass lines
up with the Earth’s magnetic field – to produce magnetic domains. Each magnetic domain is also its
Magnetic Domains

4. own tiny magnet and therefore has an N and S pole. In a piece of de-magnetized iron, the domains are
randomly oriented. In a piece of strongly magnetized iron, the domains are all aligned.
The earth is like a giant magnet!
The nickel iron core of the earth gives the earth a
magnetic field much like a bar magnet.
The Earth’s magnetism is also caused by moving electric
charges – electrons and ions – in the molten outer core
produce the magnetic field. Scientists think there are two
reasons for the movement of charges:
1. The Earth’s rotation on its axis
2. Convection current from heat rising off the solid inner
core.
Aerospce engineers design satellites to withstand the effects of the Earth’s magnetic field and
the charged particles that flow along it. The field can affect a satellite’s orientation and the
charged particles can disrupt sensitive electronics.
Types of Magnets
 Induced /Temporary Magnets become magnetized in the presence of a magnetic field. They
lose their magnetism gradually, when the magnetic field is removed. Some irons and iron alloy,
as well as paper clips and nails, function as temporary magnets
 Lodestones/Permanent magnets do not easily lose their magnetism. May be naturally –
occurring (“rare-earth”) elements, or chemical compounds. Examples include alnico (an alloy
of aluminun, nickel, and cobalt) and ferrites (ceramic-like material made from a mix of iron
oxides with nickel, strontium or cobalt.
 Commonly used Permanent magnets - Ceramic magnets – strong and work well for
most experiments. Alnico magnets – are stronger and expensive, and work very well for
science experiments. Neodymium magnets – are the strongest and most expensive of
the three.
 Electromagnets temporary magnets produced by moving electric current. Preferred for
applications that require strength including rail road tracks, motor engines, MRI machines, and
cranes. They’re also used in computer and television hardware.
Electric Current and Magnetism
Can electric current create a magnet?
A brief history:

5.  1819, Hans Christian Oersted, a Danish physicist and chemist
and a professor in the University of Copenhagen, discovered
during a class demonstration that a current carrying wire would
deflect the compass needle. He inferred that an electric current
would induce a magnetic field.
 When the switch was closed, the compass needle moved just
as if the wire were a magnet.
1820 Andre Marie Ampère finds that parallel wires carrying current
produce forces on each other.
1820s, 1830s Michael Faraday develops the concept of electric field and shows that
electric current + magnetism -> motion (motor effect)
motion + magnetism -> electric current (electromagnetic induction)
1860s James Clerk Maxwell establishes a mathematical description of electromagnetism.
Electricity and Magnetism – how are they related?
When an electric current passes through a wire a magnetic field is formed.
What is an electromagnet?
When an electric current is passed through a coil of wire wrapped around a metal core, a very strong magnetic
field is produced. This is called an electromagnet.
Magnetic field of a straight wire

6. Right hand screw rule, a.k.a. the ‘corkscrew’ or ‘pencil sharpener’ rule:
Place thumb in direction of current; fingers indicate direction of the magnetic field.
Electromagnets are created by wrapping a coil of wire around a magnetic material, usually iron or steel,
and running electricity through it. The electric current turns the magnetic material in the middle of the
coil into a magnet.
The magnetic field of an electromagnet can be turned on and off as you turn the electricity to coiled
wire on and off.
 Two wires carrying electric current exert force on each other, just like two magnets.
 The forces can be attractive or repulsive depending on the direction of current in both
wires.
The magnetic field around a single wire is too small to be of much
use.
 There are two techniques to make strong magnetic fields
from current flowing in wires:
1. Many wires are bundled together, allowing the same
current to create many times the magnetic field of a
single wire.
2. Bundled wires are made into coils which concentrate
the magnetic field in their center.
Note: Here
field lines are
closed loops.

7. Solenoid the most common form of electromagnetic device is a coil
with many turns. A coil takes advantage of these two techniques
(bundling wires and making bundled wires into coils) for increasing
field strength.
Galvanometer: A sensitive instrument used to detect electric current
– Consists of a magnetic needle centered under loops of insulated wire
– Electric current will cause the needle to pivot, detecting even very small
currents
– May be calibrated to measure current (ammeter) or voltage (voltmeter)
Some Uses of Electromagnets:
1. Magnetic memory storage – Inside a computer hard drive are disks called platters. The platters
are coated with a simple material similar to rust. When this material is exposed to a magnet, it
becomes magnetized. Many little electromagnets are used arrange, or “write” the magnetism
into specific patterns, and recognize, or “read’ it. These little electromagnets are called
“read/write heads”. They are located on an arm that moves above the disk or platter. The position
of all the little electromagnet heads in the arm over the top of the platter allows them to read and
write information to the disk. Some devices that use magnetic memory storage are computers,
flash drives, and zip or floppy disks. Credit card, debit and ATM cards also have magnetic
information storage on the dark strip or chip on one side. That magnetic strips contain bank and
account information.
Note: If you place a permanent magnet near something that provides magnetic storage, such as
hard drive, it erases the memory or stored information. In contrast, electromagnet can only erase
memory when it is turned on.
2. Engineers use magnets in all sorts of devices including motors and appliances.
3. Railroad tracks
4. MRI machines
5. Motor Engines
6. Sound recording
7. Microphones Speakers and amplifiers

8. 8. Computers and televisions
9. Refrigerators
10.Generators