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Why electromagnets over permanent magnets for a large dc machine?
Wiki User
∙ 11y ago
The flux density of an electromagnet can be easily controlled. It's also easy and cheap to produce a large flux density with an electromagnet which is necessary for such large dc motors. Permanent magnets are generally expensive. For such a large motor,a very large permanent magnet will be needed for that motor which will not be ideal.
AnswerElectromagnets are more powerful than temporary magnets, and -as pointed out above- their flux density can be controlled.
Wiki User
∙ 11y ago
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What of types of symbols would be used on an electrical drawing for a large machine?
c
Why is excitation necessary for synchronous generators?
generators work by rotating a magnetic field thru a wire shell or by rotating wire thru a stationary magnetic field (think of a small DC motor with magnets around the shell) since large generators dont have magnets in them (its not very efficent)you have to send a flowing current thru the rotating coils to produce the magnetic field. this induces current in the stator and you have a generator..of course the same effect is produced by inducing a current in the stator and pulling the output from the rotor.
What are the advantages of Swinburne's test?
1. swinburne's test is economical since power required to test a large machine is very small (i.e.,)no load input power. 2.The efficiency of the machine can be predicted at any load, since constant losses are known. 3.This method enables us to determine the losses and efficiency without actually loading the machine
What does 50db sound like?
Quiet street Normal conversation refrigerator 50 - 60 electric toothbrush 50 - 75 washing machine 50 - 75 air conditioner 50 - 80 electric shaver 40-45-hotel, theater between performances 50-65-loud conversation 40 quiet office, library 50 large office
Why is a starting current in a DC motor very high?
A rotating d.c. motor generates a back-emf which opposes the supply voltage and reduces the current drawn by the motor. When the motor is stationary, it cannot generate this back emf and, so, the only opposition to current is the resistance of its windings which is relatively low. So, on startup, the current is large; as the machine starts to run, the resulting back emf, acts to reduce the current.
Where use electromagnets?
Inside of electric motors are electromagnets and permanent magnets. In a metal junk yard large electromagnets are used to pick up metal. In MRI's large electromagnets are used for imaging.
Is an electromagnet stronger than a permanent magnet?
Not necessarily. The key difference between a permanent magnet and an electromagnet is the a permanent magnet does not change whereas an electromagnet's magnetic feild can be altered by varying the current through it. This means that electromagnets are more useful because they can be turned on or off, turned up or down or be put in 'reverse'.
What are electromagnets used to record information on?
Electromagnets...electromagnets are magnets attract, or pull, some kinds of metal objects. Stronger magnets exert a greater pull on the objects they attract. Sometimes it would be useful if you could turn off a magnet when you did not want it to attract objects. That is what an electromagnet can do. Some electromagnets .in power plants and factories electromagnets are very large. You can make a small, simple electromagnet in school or at home.
Why is a crane in a steelworks fitted with a large electromagnet?
Because they can then lift the steel easily without having to put chains and lifting gear onto it.
How does a train move on magnets?
In the case of the maglev (magnetic levitation), the train has large electromagnets in its drive section, and the track has large electromagnets along the trackway. The electromagnets in the train are energized, and the ones in the trackway below the train are energized, and this both lifts and propels (and stops) the train. The magnets in the trackway are energized along the path of the train so no energy is being used in the trackway electromagnets except the ones right below and directly in front of the train. Use the provided link to the Wikipedia article and check things out.
Can magnets lift up things?
Magnets are better used in lifting hot metals. Lifting magnets are the type of magnets that are used to lift high temperature magnetic materials.
How can a magnet lose it's magnetic?
Permanent magnets are magnetic because of things called "domains." Domains are like mini-magnets in the large magnet - when they all line up perfectly, you get a noticeable magnetic field. When they don't, the domains cancel each other out, and hence, do not create a magnet. To demagnetize a permanent magnet, the domains must come out of alignment - this is most easily accomplished by imparting a large force to the magnet (hitting it with a hammer) Alternatively, electromagnets are created via moving charges in a coil of wire (electric current). These magnets are designed to be turned on and off, so demagnetizing an electromagnet is as simple as switching off the current.
5 appliances that have magnets or electromagnets in them?
Every appliance that has a motor in it uses electromagnets. The only appliance that I can think of right now that does not use electromagnets in it is a toaster and a bus. I WANT A COOKIEAND A TOASTER
What industry use electromagnets?
Since electromagnets are used in most large electric motors,the answer is almost all industry.
What is a magnet used for in science?
Ooh, lots of things. Magnets are used everywhere. Electric motors use both permanent magnets and electromagnets made by electric current, for instance. The most impressive and scary use for magnets in science is in Linear Accelerators like the one at the Large Hadron Collider in Switzerland and France. Here, huge, scary magnets, magnets that need to be cooled with liquid helium to within 2 degrees of the coldest temperature that can exist, anywhere in the universe, control a pair of beams of tiny particles and make them travel at 299,792 km per second, or just a tiny bit slower than light itself. At that speed they make the two beams collide with each other. From what results from these collisions, they hope to find out, for instance, what makes stuff heavy, and find out more about how the universe works.
Do cars use magnets?
Most cars do not use many magnets, however, there were several experimental cars developed during the 1940s and being reexamined currently that actually run on large electromagnets. The main downfall of these cars is that they pulled down power lines and literally ripped cables up from under the road with their powerful magnetic field.
Why is steel not used to make electro magnets?
steel is note for an elecromagnet because once it turned magnetic it stays magnetic
