<< Chapter < Page Chapter >> Page >

A ferromagnetic material is a substance that shows spontaneous magnetisation.

Permanent magnets

The poles of permanent magnets

Because the domains in a permanent magnet all line up in a particular direction, the magnet has a pair of opposite poles, called north (usually shortened to N ) and south (usually shortened to S ). Even if the magnet is cut into tiny pieces, each piece will still have both a N and a S pole. These magnetic poles always occur in pairs. In nature, we never find a north magnetic pole or south magnetic pole on its own.

Magnetic fields are different from gravitational and electric fields. In nature, positive and negative electric charges can be foundon their own, but you never find just a north magnetic pole or south magnetic pole on its own. On the very small scale, zooming in to the size of atoms, magnetic fields are caused bymoving charges (i.e. the negatively charged electrons).

Magnetic attraction and repulsion

Like (identical) poles of magnets repel one another whilst unlike (opposite) poles attract. This means that two N poles or two S poles will push away from each other while a N pole and a S pole will be drawn towards each other.

Attraction and Repulsion

Like poles of magnets repel each other whilst unlike poles attract each other.

Do you think the following magnets will repel or be attracted to each other?

  1. We are required to determine whether the two magnets will repel each other or be attracted toeach other.

  2. We are given two magnets with the N pole of one approaching the N pole of theother.

  3. Since both poles are the same, the magnets will repel each other.

Got questions? Get instant answers now!

Do you think the following magnets will repel or be attracted to each other?

  1. We are required to determine whether the two magnets will repel each other or be attracted toeach other.

  2. We are given two magnets with the N pole of one approaching the S pole of theother.

  3. Since both poles are the different, the magnets will be attracted to each other.

Got questions? Get instant answers now!

Representing magnetic fields

Magnetic fields can be represented using magnetic field lines starting at the North pole and ending at the South pole. Although the magnetic field of a permanent magnet is everywhere surrounding the magnet (in all three dimensions), we draw only some of the field lines to represent the field(usually only a two-dimensional cross-section is shown in drawings).

In areas where the magnetic field is strong, the field lines are closer together. Where the field is weaker, the field lines are drawn further apart. The number of field lines drawn crossing a given two-dimensional surface is referred to as the magnetic flux . The magnetic flux is used as a measure of the strength of the magnetic field over that surface.

  1. Field lines never cross.
  2. Arrows drawn on the field lines indicate the direction of the field.
  3. A magnetic field points from the north to the south pole of a magnet.

Investigation : field around a bar magnet

Take a bar magnet and place it on a flat surface. Place a sheet of white paper over the barmagnet and sprinkle some iron filings onto the paper. Give the paper a shake to evenly distribute the iron filings. In yourworkbook, draw the bar magnet and the pattern formed by the iron filings. Draw the pattern formed when you rotate the bar magnet to a different angle asshown below.

As the activity shows, one can map the magnetic field of a magnet by placing it underneath a piece of paper and sprinklingiron filings on top. The iron filings line themselves up parallel to the magnetic field.

Investigation : field around a pair of bar magnets

Take two bar magnets and place them a short distance apart such that they are repellingeach other. Place a sheet of white paper over the bar magnets and sprinkle some iron filings onto the paper. Give the paper a shaketo evenly distribute the iron filings. In your workbook, draw both the bar magnets and the pattern formed by the iron filings. Repeatthe procedure for two bar magnets attracting each other and draw what the pattern looks like for this situation. Make a note of theshape of the lines formed by the iron filings, as well as their size and their direction for both arrangements of the bar magnet.What does the pattern look like when you place both bar magnets side by side?

As already said, opposite poles of a magnet attract each other and bringing them together causes their magnetic field lines to converge (come together). Like poles of a magnet repel each other and bringing them together causes their magnetic field lines to diverge (bend out from each other).

Ferromagnetism and retentivity

Ferromagnetism is a phenomenon shown by materials like iron, nickel or cobalt.These materials can form permanent magnets. They always magnetise so as to be attracted to a magnet, no matter whichmagnetic pole is brought toward the unmagnetised iron/nickel/cobalt.

The ability of a ferromagnetic material to retain its magnetisation after an external field is removed is called its retentivity .

Paramagnetic materials are materials like aluminium or platinum, which become magnetised in an externalmagnetic field in a similar way to ferromagnetic materials. However, they lose their magnetism when the external magnetic field is removed.

Diamagnetism is shown by materials like copper or bismuth, which become magnetised in a magnetic field with a polarity opposite to the external magnetic field. Unlike iron, they are slightly repelled by a magnet.

Questions & Answers

what is mutation
Janga Reply
what is a cell
Sifune Reply
how is urine form
Sifune
what is antagonism?
mahase Reply
classification of plants, gymnosperm features.
Linsy Reply
what is the features of gymnosperm
Linsy
how many types of solid did we have
Samuel Reply
what is an ionic bond
Samuel
What is Atoms
Daprince Reply
what is fallopian tube
Merolyn
what is bladder
Merolyn
what's bulbourethral gland
Eduek Reply
urine is formed in the nephron of the renal medulla in the kidney. It starts from filtration, then selective reabsorption and finally secretion
onuoha Reply
State the evolution relation and relevance between endoplasmic reticulum and cytoskeleton as it relates to cell.
Jeremiah
what is heart
Konadu Reply
how is urine formed in human
Konadu
how is urine formed in human
Rahma
what is the diference between a cavity and a canal
Pelagie Reply
what is the causative agent of malaria
Diamond
malaria is caused by an insect called mosquito.
Naomi
Malaria is cause by female anopheles mosquito
Isaac
Malaria is caused by plasmodium Female anopheles mosquitoe is d carrier
Olalekan
a canal is more needed in a root but a cavity is a bad effect
Commander
what are pathogens
Don Reply
In biology, a pathogen (Greek: πάθος pathos "suffering", "passion" and -γενής -genēs "producer of") in the oldest and broadest sense, is anything that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ. The term pathogen came into use in the 1880s.[1][2
Zainab
A virus
Commander
Definition of respiration
Muhsin Reply
respiration is the process in which we breath in oxygen and breath out carbon dioxide
Achor
how are lungs work
Commander
where does digestion begins
Achiri Reply
in the mouth
EZEKIEL
what are the functions of follicle stimulating harmones?
Rashima Reply
stimulates the follicle to release the mature ovum into the oviduct
Davonte
what are the functions of Endocrine and pituitary gland
Chinaza
endocrine secrete hormone and regulate body process
Achor
while pituitary gland is an example of endocrine system and it's found in the Brain
Achor
what's biology?
Egbodo Reply
Biology is the study of living organisms, divided into many specialized field that cover their morphology, physiology,anatomy, behaviour,origin and distribution.
Lisah
biology is the study of life.
Alfreda
Biology is the study of how living organisms live and survive in a specific environment
Sifune
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play Download on the App Store Now




Source:  OpenStax, Siyavula textbooks: grade 10 physical science. OpenStax CNX. Aug 29, 2011 Download for free at http://cnx.org/content/col11245/1.3
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Siyavula textbooks: grade 10 physical science' conversation and receive update notifications?

Ask