There are many different types of permanent magnet materials , each with their own unique characteristics. Each material has a family of grades that have properties slightly different from each other, though based on the same composition. Modern permanent magnets are made of special alloys that have been found through research to create increasingly better magnets. The most common families of permanent magnet materials today are made out of aluminum-nickel-cobalt alnicos , strontium-iron ferrites, also known as ceramics , neodymium-iron-boron a.
The samarium-cobalt and neodymium-iron-boron families are collectively known as the rare-earths. Rare Earth magnets are magnets that are made out of the rare-earth group of elements. The most common rare-earth magnets are the neodymium-iron-boron neo magnets and samarium cobalt SmCo magnets. Soft iron and certain iron alloys, such as p ermalloy a mixture of iron and nickel can be very easily magnetized, even in a weak field.
As soon as the field is removed, however, the magnetism is lost. These materials make excellent temporary magnets, like those used in telephones and electric motors.
Electromagnets are used when very strong magnets are required. Electromagnets are produced by placing a metal core usually an iron alloy inside a coil of wire that carries an electric current.
The electricity in the coil produces a magnetic field. The strength of the electromagnet depends on the strength of the electric current and the number of coils of wire. Its polarity depends on the direction of the current flow.
While the current flows, the core behaves like a magnet, but as soon as the current stops, the magnetic properties are lost. Electric motors , televisions, maglev trains, telephones, computers, and many other modern devices use electromagnets.
These are electrical currents that are induced when a magnetic field moves in relation to an electrical conductor that has been placed within reach of the magnetic field. In turn, these eddy currents create a magnetic field that acts to stop the relative motion of the original magnetic field and electrical conductor. Magnet materials can vary significantly in cost from one to the other.
Here is an approximate guide as to magnet costs:. On a cost-per-pound basis neodymium magnets may seem very costly. However, on a cost per BHmax basis, they are not so costly. Using a more powerful magnet, enables the entire device that the magnet goes into to be miniaturized. This yields cost savings that favor more powerful magnet materials.
Both of these associations are now a part of the International Magnetics Association. Some of the publications and standards produced by these organizations are reproduced here for your convenience. To efficiently order magnets, you need to have a good idea of what you want to accomplish. Here are a few items to consider:. If stored away from factors that adversely affect the magnet such as power lines, other magnets, high temperatures etc. Shock and vibration do not affect modern magnet materials , unless sufficient to physically damage the material.
Modern magnet materials do lose a very small fraction of their magnetism over time. The most powerful magnets available today are the rare- earth types. Of the rare-earths, neodymium magnets are the strongest. 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. Relays are electrically operated switches.
They use an electromagnet, often to control a high-power circuit using a low-power signal or where multiple circuits need to be controlled by one circuit. The electromagnet inside the gray transformer makes it possible to transfer the electrical current, which is typically a much higher voltage in the power distribution grid.
The site receiving electricity gets it at a lower voltage. As a journalist and editor for several years, Laurie Brenner has covered many topics in her writings, but science is one of her first loves. Her stint as Manager of the California State Mining and Mineral Museum in California's gold country served to deepen her interest in science which she now fulfills by writing for online science websites.
Brenner is also a published sci-fi author. She graduated from San Diego's Coleman College in What Devices Use Electromagnets? TL;DR Too Long; Didn't Read Some everyday devices that have electromagnets inside them include: Microphones, speakers, headphones, telephones and loudspeakers Electric motors and generators Doorbells and electric buzzers Computer hard drives Multiple household appliances.
Related Articles Everyday Uses of Magnets. The above formula can rearranged as shown below:. From this formula, it is evident that-" Current varies directly as the voltage and inversely as the resistance ". The formula can also be arranged to find out the resistance in a circuit if the voltage and current are known.
Practical Resistors: The resistance of a material depends on four physical factors: 1 The type of material from which it is made. For example copper and silver are very good conductors of electric current, but iron is six times lesser in its conductivity than them.
So each material has a specific resistance inherent in them. The specific resistance of a material is the number of ohms in a 1 foot long 0. Silver has the least specific resistance, i. Wire-wound resistor : Nicrome or german silver wires are wound on a tubular ceramic form to make wire-wound resistor.
Carbon resistor: Powedered carbon is mixed with a binding material and baked into small, hard tubes with wire attached to each end to make carbon resistors. The percentage of carbon in the mixture determines the resistance value in ohms. Colour codes of resistors Carbon resistors are colour coded to indicate their values. Each resistor has four colour bands on its body. The first band the band which is nearest to the end of the resistor is the first number. The second band is the second number.
The third band is the multiplier, i. Resistors having values lower than 10 W have three colour bands. The third band is either golden or silver in colour. A golden band indicates that the first two numbers are to be multiplied by 0. A silver band indicates multiplication by 0. A circuit has a resistance of ohms and voltage applied across the circuit is 20 volts. What is the amount of current flowing through it? Find out the voltage required to produce 3 A of current through a 50 W ohms resistor.
Power and Energy:. As mentioned above, heat is developed in the load resistor as a result of current flowing through it. In absence of the load, a battery despite having the electro motive force EMF , cannot produce movement of electrons and no electrical work is accomplished.
When there is a load across the battery, movement of electrons take place. The product of the EMF in volts and movement of electrons in amperes gives us the amount of electrical work accomplished whose unit is watt W. So, 1 V causing 1 A to flow through a 1 W resistor produces 1 W of power. The above formula can also be expressed as. Questions: 1.
Find out the heat dissipated by a 50 W resistor when 0. Find out the power dissipated by a 10, W resistor connected across a voltage source of V. Find out the maximum voltage that may be connected across a 20 W, W resistor. Find out the maximum current that can flow through a W 1 W resistor.
We have,. What are conductors? Matters which allow the flow of electric current through them are called conductors. Metals are known to be good conductors, with copper and silver among the best. The conductivity of a particular material depends on the number of free electrons present in it. A conductor may be a very good conductor, a fairly good conductor or a poor conductor.
So, a greater conductivity or conductance implies lesser resistance and a lesser conductivity implies greater resistance.
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