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Author Topic: How is electromagnetic force a long range force ?  (Read 919 times)

Offline Dr Amrutha

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Electromagnetic force operates between charged particles such as proton and electron,If that is the case how can it be classified as long range force that is it can operate over a long distance ? Isn't charged particles at the atomic level(small distance between proton and electron)  which should make electromagnetic force a short range force ?


 

Offline Atomic-S

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Re: How is electromagnetic force a long range force ?
« Reply #1 on: 20/04/2016 06:26:45 »
When electrons and protons are together in equal numbers in an atom, the electromagnetic force is quite powerful between them, but at points well outside of the atom, the effects of the positive and negative particles, coming from about the same direction and distance from the standpoint of the external observer,  mostly cancel out and therefore are nullified for points well outside the atom. Although there are exceptions:  in iron, for example, the magnetic dipole moments of spinning electrons within one crystal grain are compelled by the arrangement of available energy states, due to the crystallography etc.,  to align, and there is no opposing magnetic moments, with the result that the magnetic effects do indeed extend substantially beyond the material.  The electrostatic effects of course still cancel.  However, in an electret, there is an excess of positive or negative charge, resulting in the effects of the unbalanced charge extending well beyond the material.  Thus, the electromagnetic force is indeed a long-range force, but in ordinary matter is  usually balanced so that there are very few external effects.
 

Offline PmbPhy

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Re: How is electromagnetic force a long range force ?
« Reply #2 on: 20/04/2016 06:34:33 »
Quote from: Dr Amrutha
Electromagnetic force operates between charged particles such as proton and electron,If that is the case how can it be classified as long range force that is it can operate over a long distance ?
The term long range force means that force never becomes zero at infinity. The gravitational force and the Coulomb force are both examples. The force between two objects drops off as 1/r2. However a short range force drops off much faster and is zero for all practical purposes a short distance away. E.g. the strong force between two nucleons is effectively zero at a distance of the diameter of one nucleon.

Just because a force is a long range force it doesn't mean that it only acts over large distances.

Quote from: Dr Amrutha
Isn't charged particles at the atomic level(small distance between proton and electron)  which should make electromagnetic force a short range force ?
No. You're just being confused by the name of the terms short and long range forces, that's all.
 

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Re: How is electromagnetic force a long range force ?
« Reply #2 on: 20/04/2016 06:34:33 »

 

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