Comments on: Common Misconceptions: Work Done by Magnetic Field http://www.ilovephysics.com/2009/04/20/common-misconceptions-work-done-by-magnetic-field/ Physics education research, electronic materials, and the musings of Christopher Moore, Ph.D. Wed, 01 Feb 2012 06:20:24 +0000 hourly 1 http://wordpress.org/?v= By: Vipul http://www.ilovephysics.com/2009/04/20/common-misconceptions-work-done-by-magnetic-field/comment-page-1/#comment-91167 Vipul Mon, 08 Aug 2011 18:59:46 +0000 http://www.ilovephysics.com/?p=231#comment-91167 HI! I wanted to ask that in the case of motional emf, or more elaborately, when a thin metallic wire is moving with a velocity v in a direction perpendicular to the direction (say downwards into the plane of paper) of magnetic field, there is an induced emf in the wire, which results from the displacement of electrons apparently in the direction of magnetic force. Now this should have some work being done on the electron, but you said above that no work is done? How is it so? HI! I wanted to ask that in the case of motional emf, or more elaborately, when a thin metallic wire is moving with a velocity v in a direction perpendicular to the direction (say downwards into the plane of paper) of magnetic field, there is an induced emf in the wire, which results from the displacement of electrons apparently in the direction of magnetic force. Now this should have some work being done on the electron, but you said above that no work is done? How is it so?

]]> By: Arghyadeep giri http://www.ilovephysics.com/2009/04/20/common-misconceptions-work-done-by-magnetic-field/comment-page-1/#comment-91166 Arghyadeep giri Fri, 05 Aug 2011 20:23:44 +0000 http://www.ilovephysics.com/?p=231#comment-91166 hi this is Arghyadeep from INDIA.IM A STUDENT OF PHYSICS.I just wanted to know that if the work done on the charged particle by a magnet is zero then what is doing the work in case of attraction of a magnetic material.I mean what is the physics behind work done by a magnet in case of ATTRACTION OF A MAGNETIC MATERIAL. IS THERE ANY RELATION WITH THE EDDY CURRENTS IN CASE OF WORK DONE IN THIS CASE? I just want to know the real physics behind it.cross and dot products are simple mathematical approach towards the subject.ill be glad if i get an answer.thanks. hi this is Arghyadeep from INDIA.IM A STUDENT OF PHYSICS.I just wanted to know that if the work done on the charged particle by a magnet is zero then what is doing the work in case of attraction of a magnetic material.I mean what is the physics behind work done by a magnet in case of ATTRACTION OF A MAGNETIC MATERIAL.
IS THERE ANY RELATION WITH THE EDDY CURRENTS IN CASE OF WORK DONE IN THIS CASE?
I just want to know the real physics behind it.cross and dot products are simple mathematical approach towards the subject.ill be glad if i get an answer.thanks.

]]> By: Christopher Moore http://www.ilovephysics.com/2009/04/20/common-misconceptions-work-done-by-magnetic-field/comment-page-1/#comment-91152 Christopher Moore Wed, 06 Jul 2011 13:53:03 +0000 http://www.ilovephysics.com/?p=231#comment-91152 Nope. By definition, the velocity vector is <em>always</em> perpendicular to the magnetic force vector. Of course, the magnetic field vector and the velocity vector can share some non-perpendicular component, but the nature of the cross-product insures that the magnetic force is perpendicular to both at all times. You cannot just add an acceleration vector (essentially the force) and a velocity vector. The resultant would be meaningless, having units of m/s*(1+1/s). An acceleration (such as the change in direction you mention) only indicates the presence of a force, not necessarily that work has been done. Nope. By definition, the velocity vector is always perpendicular to the magnetic force vector. Of course, the magnetic field vector and the velocity vector can share some non-perpendicular component, but the nature of the cross-product insures that the magnetic force is perpendicular to both at all times.

You cannot just add an acceleration vector (essentially the force) and a velocity vector. The resultant would be meaningless, having units of m/s*(1+1/s).

An acceleration (such as the change in direction you mention) only indicates the presence of a force, not necessarily that work has been done.

]]> By: Saurabh Suman http://www.ilovephysics.com/2009/04/20/common-misconceptions-work-done-by-magnetic-field/comment-page-1/#comment-91151 Saurabh Suman Tue, 05 Jul 2011 12:16:08 +0000 http://www.ilovephysics.com/?p=231#comment-91151 Sir i have a little doubt on what you explained above. You said "The particle is moving in the direction of the velocity, so the displacement vector will be in the same direction",but actually the particle will experience magnetic forces also,so it will move in a direction resultant of the both (the velocity vector and magnetic force vector) and hence there will be certain angle b/w magnetic force and displacement vector,and hence word done is not zero. In short what i m saying is magnetic forces are capable of changing direction of charged particle and hence it must have some effect on the work done. Hoping for your response :) Sir i have a little doubt on what you explained above.
You said “The particle is moving in the direction of the velocity, so the displacement vector will be in the same direction”,but actually the particle will experience magnetic forces also,so it will move in a direction resultant of the both (the velocity vector and magnetic force vector) and hence there will be certain angle b/w magnetic force and displacement vector,and hence word done is not zero.
In short what i m saying is magnetic forces are capable of changing direction of charged particle and hence it must have some effect on the work done.
Hoping for your response :)

]]> By: Christopher Moore http://www.ilovephysics.com/2009/04/20/common-misconceptions-work-done-by-magnetic-field/comment-page-1/#comment-91135 Christopher Moore Fri, 22 Apr 2011 14:29:19 +0000 http://www.ilovephysics.com/?p=231#comment-91135 A magnet does not attract all metals. Try sticking a magnet to a piece of aluminum or some really crappy steel. A magnet does not attract all metals. Try sticking a magnet to a piece of aluminum or some really crappy steel.

]]> By: Ahmed http://www.ilovephysics.com/2009/04/20/common-misconceptions-work-done-by-magnetic-field/comment-page-1/#comment-90888 Ahmed Tue, 29 Dec 2009 21:56:42 +0000 http://www.ilovephysics.com/?p=231#comment-90888 plz i need an answer to this question (ASAP) the question is : *How a magnet attract metals ? i mean by this question the following that magnet attract due to the current in atoms due to electron rotaion so i have moving charges this moving charges the magnet make force on it this force does no work so from where the metal gain K.E *also i have anther case in need to be defiend the electrical motor also we gain energy from it by appling magnatic field and if the electric field do the work i need a prove that the enrgy gain = the energy supplied by the electric field and an application to low of conservation of energy AND THANKS plz i need an answer to this question (ASAP) the question is :
*How a magnet attract metals ?
i mean by this question the following that magnet attract due to the current in atoms due to electron rotaion so i have moving charges this moving
charges the magnet make force on it this force does no work so from where the
metal gain K.E
*also i have anther case in need to be defiend the electrical motor also we gain energy from it by appling magnatic field
and if the electric field do the work i need a prove that the enrgy gain = the
energy supplied by the electric field and an application to low of conservation
of energy
AND THANKS

]]> By: ratheesh http://www.ilovephysics.com/2009/04/20/common-misconceptions-work-done-by-magnetic-field/comment-page-1/#comment-90372 ratheesh Wed, 29 Apr 2009 18:35:31 +0000 http://www.ilovephysics.com/?p=231#comment-90372 hello, the abve idea is very good.it leads for me a refreshment for the basics thank u sir hello,
the abve idea is very good.it leads for me a refreshment for the basics
thank u sir

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