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Magnetism

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15 Oct 2009 06:39:40 IST

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The most basic ques in magnetism- What happens to the electron orbiting around th

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The most basic ques in magnetism- What happens to the electron orbiting around the nucleus,when an atom experiences a magnetic field?the magnetic field is perpendicular to the velocity of the electron and its plane of rotation.

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Deepak Shivadas

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15 Oct 2009 06:54:33 IST

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Sorry-the diagram I prepared is not uploading-however,the Lorentz force on the electron is found to act in the direction of centripital force on it,ie,the centripital force increases.

So,will the velocity of the electron increase or its radius decrease?

Remember that circumference of the electron's orbit should be an integral multiple of its wavelength,which is given by- h/mv

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Blazing goIITian

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15 Oct 2009 09:52:19 IST

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Nice question.The lorentz force on the electron will be towards the centre of its circular path. As the force is perpendicular to the velocity ,the direction changes i.e.the radius decreases. The velocity remains the same. This way the electron should collapse with the nucleus. Now this thing is not true in practical life. It is because here we have assumed that electron move around the nucleus in circular orbit which itself is not true. The trajectory of electron is not exactly known to us. Rate if satisfied.

Deepak Shivadas

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16 Oct 2009 06:51:53 IST

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Yeah,that is right,but we always assume the electron's path to be circular in physics,for eg,while calculating value of Bohr magnetone in magnetism.

However,in a reference book(ABC of physics),I noticed that they have explained diamagnetism by telling that when a magnetic field is applied,the centripital force increases on the electron,leading to an increase in its velocity and hence magnetic moment,while centripital force on the other electron,which is its pair decreases,hence decreasing the magnetic moment in its direction.The argument is that there is a net magnetic moment in one direction.But isn't it impossible for Lorentz force to increase kinetic energy?

Well, I have only agreed with your answer,but would certainly give you a hats off if you explain diamagnetism satisfactorily.

Everyone please try!

Deepak Shivadas

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18 Oct 2009 11:14:19 IST

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Noone interested?Please try to explain.Just type whatever you think.

I am waiting.....

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Blazing goIITian

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18 Oct 2009 11:34:28 IST

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What i think is that the increase in the centripetal force can't increase the velocity it can just change its direction. Secondly, if we follow the bohr's model of atom ,two paired electrons will be revolving in the same orbit. So centripetal force will be same for both of them.

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Blazing goIITian

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18 Oct 2009 11:41:40 IST

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As far as diamagnetism is concerned, the external magnetic changes the orbital velocity of the electrons in such a way that the dipoles oppose the field. Hence a repulsive interaction is created.

Deepak Shivadas

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18 Oct 2009 12:48:52 IST

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Please explain what you mean by changing the orbital velocity in 'such a way'.Does it increase or decrease or what?

Deepak Shivadas

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28 Feb 2010 07:48:48 IST

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If there is a change in speed of a particle, surely some force would be causing it. What is the force in this case?

Yasin

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28 Feb 2010 20:07:44 IST

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Hi Deepak!.. What you aim to understand is, as u rightly said, the fundamental concept of diamagnetism (and following that, paramagnetism and so on). Do u have th Resnick-Halliday book? It explains this particular thing extremely well. Get hold of the book if u can (coz that's THE best option, trust me) or I can tell u what understood frm th same. It'll need a drawing i think. Nudge me.

Yasin

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28 Feb 2010 20:33:19 IST

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If u want to think a bit more urself, heres a hint::it involves LENz's LAW.As fr which force causes th electron to change its speed (energy more appropiately), its is a consequence of Lenz's law and that is a consequence of conservation of energy (which, strangely, has never been theoretically 'proven'!!). More specifically, in this case, it is simply magentic force. (I find it better to think this way:: the external magnetic field A causes a change in the electron movement, which alters the magentic field B of the moving electron, which is a current element, in such a way that A opposes B).I hope that helps.

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