There are various types of magnets depending on their properties. Some of the most well known are listed below.

Permanent Magnets

These are the most common type of magnets that we know and interact with in our daily lives. E.g.; The magnets on our refrigerators. These magnets are permanent in the sense that once they have been magnetized they retain a certain degree of magnetism. Permanent magnets are generally made of ferromagnetic material. Such material consists of atoms and molecules that each have a magnetic field and are positioned to reinforce each other.

Classification

Permanent Magnets can further be classified into four types based on their composition: 1. Neodymium Iron Boron (NdFeB or NIB) 2. Samarium Cobalt (SmCo) 3. Alnico 4. Ceramic or Ferrite

NIB and SmCo are the strongest types of magnets and are very difficult to demagnetize. They are also known as rare earth magnets since their compounds come from the rare earth or Lathanoid series of elements in the periodic table. The 1970s and 80s saw the development of these magnets.

Alnico is a compound made of ALuminium, NIckel and CObalt. Alnico magnets are commonly used magnets and first became popular around the 1940s. Alnico magnets are not as strong as NIB and SmCo and can be easily demagnetized. This magnet is however, least affected by temperature. This is also the reason why bar magnets and horseshoes have to be taken care of to prevent them from loosing their magnetic properties.

The last type of permanent magnets, Ceramic or Ferrite magnets are the most popular today. They were first developed in the 1960s. These are fairly strong magnets but their magnetic strength varies greatly with variations in temperature.

Permanent Magnets can also be classified into Injection Moulded and Flexible magnets. Injection molded magnets are a composite of various types of resin and magnetic powders, allowing parts of complex shapes to be manufactured by injection molding. The physical and magnetic properties of the product depend on the raw materials, but are generally lower in magnetic strength and resemble plastics in their physical properties. Flexible magnets are similar to injection molded magnets, using a flexible resin or binder such as vinyl, and produced in flat strips or sheets. These magnets are lower in magnetic strength but can be very flexible, depending on the binder used.

Shape & Configuration

Permanent magnets can be made into any shape imaginable. They can be made into round bars, rectangles, horseshoes, donuts, rings, disks and other custom shapes. While the shape of the magnet is important aesthetically and sometimes for experimentation, how the magnet is magnetized is equally important. For example: A ring magnet can be magnetized S on the inside and N on the outside, or N on one edge and S on the other, or N on the top side and S on the bottom. Depending on the end usage, the shape and configuration vary.

Demagnetization

Permanent magnets can be demagnetized in the following ways: - Heat - Heating a magnet until it is red hot makes it loose its magnetic properties. - Contact with another magnet - Stroking one magnet with another in a random fashion, will demagnetize the magnet being stroked. - Hammering or jarring will loosen the magnet's atoms from their magnetic attraction.

Temporary Magnets

Temporary magnets are those that simply act like permanent magnets when they are within a strong magnetic field. Unlike permanent magnets however, they loose their magnetism when the field disappears. Paperclips, iron nails and other similar items are examples of temporary magnets. Temporary magnets are used in telephones and electric motors amongst other things.

Electromagnets

Had it not been for electromagnets we would have been deprived of many luxuries and necessities in life including computers, television and telephones. Electromagnets are extremely strong magnets. They are produced by placing a metal core (usually an iron alloy) inside a coil of wire carrying an electric current. The electricity in the current produces a magnetic field. The strength of the magnet is directly proportional to the strength of the current and the number of coils of wire. Its polarity depends on the direction of flow of current. While the current flows, the core behaves like a magnet. However, as soon as the current stops, the core is demagnetized.

Electromagnets are most useful when a magnet must be switched on and off as in large cranes used to lift cables and rods in construction.

Superconductors

These are the strongest magnets. They don't need a metal core at all, but are made of coils of wire made from special metal alloys which become superconductors when cooled to very low temperatures.

Posted by Jay Roberts at 04:25 AM | Permalink

Magnetic Effect Of Current Or Electromagnetism

The term "magnetic effect of current" means that "a current flowing in a wire produces a magnetic field around it". The magnetic effect of current was discovered by Oersted in 1820. Oersted found that a wire carrying a current was able to deflect a magnetic needle. Now, a magnetic needle can only be deflected by a magnetic field. Thus it was concluded that a current flowing in a wire always gives rise to a magnetic field round it. The magnetic effect of current is called electromagnetism which means that electricity produces magnetism.

Tenets Of Electromagnetism:

Magnetic Field Pattern Due To Straight Current-Carrying Conductor

The magnetic lines of force round a straight conductor carrying current are concentric circles whose centers lie on the wire.

The magnitude of magnetic field produced by a straight current-carrying wire at a given point is:

1. Directly proportional to the current passing in the wire, and
2. Inversely proportional to the distance of that point from the wire.

So, greater the current in the wire, stronger will be the magnetic field produced. And greater the distance of a point from the current-carrying wire, weaker will be the magnetic field produced at that point.

Magnetic Field Pattern Due To A Circular Coil Carrying Current

We know that when a current is passed through a straight wire, a magnetic field is produced around it. It has been found that the magnetic effect of current increases if, instead of using a straight wire, the wire is converted into a circular coil. A circular coil consists of twenty or more turns of insulated copper wire closely wound together. When a current is passed through a circular coil, a magnetic field is produced around it. The lines of force are circular near the wire, but they become straight and parallel towards the middle point of the coil. In fact, each small segment of the coil is surrounded by such magnetic lines of force. At the center of the coil, all the lines of force aid each other due to which the strength of the magnetic field increases.

The magnitude of magnetic field produced by a current carrying wire at its center is:

1. Directly proportional to the current passing through the circular wire, and
2. Inversely proportional to the radius of the circular wire.

A current carrying circular wire (or coil) behaves as a thin disc magnet, whose one face is a north pole and the other face is a south pole.

The strength of magnetic field produced by a current carrying circular coil can be increased

1. By increasing the number of turns of wire in the coil
2. By increasing the current flowing through the coil
3. By decreasing the radius of the coil.

Solenoids

The solenoid is a long coil containing a large number of close turns of insulated copper wire. The magnetic field produced by a current carrying solenoid is similar to the magnetic field produced by a bar magnet. The lines of magnetic force pass through the solenoid and return to the other end. If a current carrying solenoid is suspended freely, it comes to rest pointing North and South like a suspended magnetic needle. One end of the solenoid acts like a N-pole and the other end a S-pole. Since the current in each circular turn of the solenoid flows in the same direction, the magnetic field produced by each turn of the solenoid adds up, giving a strong resultant magnetic field inside the solenoid. A solenoid is used for making electromagnets.

The strength of magnetic field produced by a current carrying solenoid is:

1. Directly proportional to the number of turns in the solenoid
2. Directly proportional to the strength of current in the solenoid
3. Dependent on the nature of "core material" used in making the solenoid. The use of soft iron rod as core in a solenoid produces the strongest magnetism.

Electromagnet:

An electric current can be used for making temporary magnets known as electromagnets. An electromagnet works on the magnetic effect of current. It has been found that if a soft iron rod called core is placed inside a solenoid, then the strength of the magnetic field becomes very large because the iron ore is magnetized by induction. This combination of a solenoid and a soft iron core is called an electromagnet. Thus, an electromagnet consists of a long coil of insulated copper wire wound on a soft iron core.

The electromagnet acts as a magnet only so long as the current is flowing in the solenoid. The moment the current is switched off the solenoid is demagnetized. The core of the electromagnet must be of soft iron because soft iron loses all of its magnetism when current in the coil is switched off. Steel is not used in electromagnets, because it does not lose all its magnetism when the current is stopped and becomes a permanent magnet.

Electromagnets can be made of different shapes and sizes depending on the purpose for which they are to be used.

Factors Affecting The Strength Of An Electromagnet:

The strength of an electromagnet is: 1) Directly proportional to the number of turns in the coil. 2) Directly proportional to the current flowing in the coil. 3) Inversely proportional to the length of air gap between the poles.

In general, an electromagnet is often considered better than a permanent magnet because it can produce very strong magnetic fields and its strength can be controlled by varying the number of turns in its coil or by changing the current flowing through the coil.

Posted by Jay Roberts at 04:24 AM | Permalink

Uses Of Magnets in Industry

From Lodestone being used as a mariner's compass to magnetic therapy - magnets have come a long way. Magnets are used in various industries all over the world in various forms.

In Medicine And Health:

Magnetic-Therapy

Old Chinese texts dating back to 2000 B.C. make references to the application of lodestones at acupuncture sites. Similarly, Hindu scriptures of the 40th century mention the treatment of diseases with lodestones. The Greeks called them lapus-vivas (live-stones) and drew them from the fields rich in deposits of magnetic stones in southern Greece. The Egyptians ascribed a variety of therapeutic uses to lodestones. Electric eels and fish were used by Romans to treat arthritis and gout, and medieval doctors reported that magnets could cure melancholy, arthritis and baldness. Somewhere along the line, cynicism stepped in and medical science refuted the use of magnets. However, magnetic therapy was revived in the late 19th century and today Tectonic magnets are regularly used by golf, baseball and football sports celebrities for pain relief.

Magnets are also placed on insoles of shoes, and designed in a manner so as to access acupressure points on the soles of the feet. This provides great relief to the feet and rejuvenates them on long walks.

Magnetic mattress pads are also believed to be very relaxing for the body and especially aid insomniacs. Magnetic beds apparently calm the nervous system and bring emotional and physical relaxation to the body. MRIs and X-rays: While magnetic therapy has been awarded the status of 'alternate medicine' not even the most stringent scientists can deny the use of magnets in X-rays and MRIs. In the 1900's Edward M Purcell and Felix Bloch, both American physicists, developed a way to measure the magnetic field of the nuclei. This discovery led to MRI also known as Magnetic Resonance Imaging. While X-rays still remain the most popular method for a quick look under the skin, MRI machines that are used in hospitals make use of the way that tissues inside our bodies respond to magnetic fields in order to see more details than x-rays can. Brain scans and heart scans are no longer to be feared and indeed for doctors this is a gift from heaven! In Electronics

Televisions

Televisions have magnets inside of them that make them work. These cathode ray tubes have an electron gun in the neck of the tube that shoots a stream of electrons toward the screen. Normally these electrons travel in a straight line and strike the screen at a central spot.

But powerful electromagnets in the tube's neck deflect the electrons toward the top or bottom and left or right sides of the tube. The inside of the screen has a special coating that glows when the stream of electrons strikes it. In this way, magnets help us see images on the TV screen.

Computer Disks

Computer storage disks are coated with an iron material that stores tiny magnetic fields in a pattern, and that is how we store data on the computer disks. Computer screens also use magnets in a manner similar to televisions.

Video Tapes

Video tapes also use a similar material with iron compounds that allows magnetic fields to be stored in patterns on the tape.

In Industry

Magnetic Sweepers

Magnetic sweepers are used in industries to help reduce maintenance costs and eliminate flat tires at airports, loading docks and work sites.

Sorters

Magnets can also be used for sorting magnetic material from non-magnetic material. Magnets are used in the mining industry to separate metals from ore. Food manufacturers use magnets to prevent small iron particles from mixing with the food. Similarly vendors use magnets to separate coins from other junk.

Separation

Various kinds of magnetic conveyors, plates, separators, pulleys and grates are used to separate impure, ferrous material from high volume industrial flow. Similar magnets are also used to recover ferrous objects from ocean depths.

Miscellaneous:

Maglev Trains

Maglev trains operate without wheels as they 'float' above the track due to magnetic repulsion between electromagnets in the track and underside of the train. Maglev trains can travel very fast, up to 480 km/h (300 mph). These Maglev trains were launched in Japan, in 1997, and clocked at an incredible 343 miles an hour!

Credit Cards and Other ID Cards

Magnets are also used to make the everyday credit cards and other forms of ID that we use.

Around the house

Magnets are used around the house in innumerable things some of which are: Headphones, Stereo speakers, Computer speakers, Telephone receivers, Phone ringers, Microwave tubes, Doorbell ringer solenoid, Refrigerator magnets to hold things, Seal around refrigerator door, Plug-in battery eliminators, TV deflection coil, TV degaussing coil, Computer monitor deflection coil, Computer hard drive recording and reading head, Dishwasher water valve solenoid, Shower curtain weights / attach to tub, Power supply transformers and many more!

Posted by Jay Roberts at 04:21 AM | Permalink

Magnetic Axis And Geographic Axis

A freely suspended magnet always points in the North-South direction even in the absence of any other magnet. This suggests that the Earth itself behaves as a magnet which causes a freely suspended magnet (or magnetic needle) to point always in a particular direction: North and South. The shape of the Earth's magnetic field resembles that of a bar magnet of length one-fifth of the Earth's diameter buried at its center.

The South Pole of the Earth's magnet is in the geographical North because it attracts the North Pole of the suspended magnet and vice versa. Thus, there is a magnetic S-pole near the geographical North, and a magnetic N-pole near the geographical South. The positions of the Earth's magnetic poles are not well defined on the globe; they are spread over an area. The axis of Earth's magnet and the geographical axis do no coincide. The axis of the Earth's magnetic field is inclined at an angle of about 15o with the geographical axis. Due to this a freely suspended magnet makes an angle of about 15o with the geographical axis and points only approximately in the North-South directions at a place. In other words, a freely suspended magnet does not show exact geographical South and North because the magnetic axis and geographical axis of the Earth do not coincide.

Cause Of Earth's Magnetism:

It is now believed that the Earth's magnetism is due to the magnetic effect of current which is flowing in the liquid core at the center of the Earth. Thus, the Earth is a huge electromagnet.

Elements Of Earth's Magnetic Field

To understand the Earth's magnetic field at any place, we should know the following two quantities or elements

1. Declination
2. Angle of dip (or Inclination)

Declination

The vertical plane passing through the axis of a freely suspended magnet is called magnetic meridian. The direction of Earth's magnetic field lies in the magnetic meridian and may not be horizontal. The vertical plane passing through the true geographical North and South (or geographical axis of Earth) is called geographical meridian. The angle between the magnetic meridian and the geographic meridian at a place is called declination at that place.

The value of the angle of declination is different at different places on Earth. To find the exact geographic directions (North and South) at a place by using a magnetic compass, we should know the angle of declination at that place. The declination is expressed in degrees East (o E) or degrees West (o W). For example a declination of 2 o E means the compass will point 2 degrees east of true geographical North. Thus, the knowledge of declination at a place helps in finding the true geographical directions at that place. In every map used by surveyors, mariners and air pilots, declination for different places is indicated. It should be noted that at the places of zero declination, the compass North will coincide with the true geographical North.

Angle Of Dip Or Inclination

So far we have only considered one type of magnetic needle which can move only in the horizontal place and points approximately in the North-South direction. Now, if we take a magnetic needle which is free to rotate in the vertical plane, then it will not remain perfectly horizontal. The compass needle makes a certain angle with the horizontal direction. In fact, in the Northern Hemisphere of Earth, the North Pole of the magnetic needle dips below the horizontal line. At any place, the magnetic needle points in the direction of the resultant intensity of Earth's magnetic field at the place.

Angle of Dip at the Poles

The magnetic lines of force at the poles of Earth are vertical due to which the magnetic needle becomes vertical. The angle of dip at the magnetic poles of Earth is 90 o.

Angle of Dip at the Equator

The lines of force around the magnetic equator of the Earth are perfectly horizontal. So the magnetic needle will become horizontal there. Thus, the angle of dip at the magnetic equator of the Earth will be 0 o. The angle of dip varies from place to place.

Posted by Jay Roberts at 04:20 AM | Permalink