In mechanism of electricity in conductors my teacher said the free electrons collide with positive lattice and this positive lattice is oscillating about its mean position. Ok for producing current battery is used. Now my question is why this positive lattice oscillate about a mean position and why it cannot move freely like electrons and if it is positively charged why it cannot go to negative terminal of the battery .my teacher also said that free electrons undergo zig zag motion after colliding and my question is why?
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$\begingroup$ This question does not show any research effort. $\endgroup$– Alfred CentauriCommented May 6, 2018 at 2:38
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$\begingroup$ Means you are saying there is no explanation of the question's?? $\endgroup$– SAHILCommented May 6, 2018 at 7:05
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This is a very good question, and one that is very hard to give a good complete answer. The answer is the entire field of solid state physics.
It's a bit of luck, or a mystery, as to why we can understand it at all. Nature has arranged things so that the positive charges are firmly held in place by chemical bonds, which of course, comprise electrons. But in some materials (metals, for example), the "outermost" electrons are not so involved in bonding, and move through the solid almost as if there were no positive charges at all. Almost. Electric fields accelerate the charges as if they were free. But of course, if the electrons were completely free, they would accelerate without bound in the presence of the field.
The electrons are not completely free. In an ideal crystal, they would act as if they were completely free. But no solid is perfect. For one, there are always impurities. The accelerating electrons hit them, and can be imagined to stop, and start from zero velocity again, accelerating until it hits the next impurity. In consequence, the electron has a steady average velocity, a velocity that does not increase without bound. That's a very crude model, but it does a surprisingly good job of helping to understand what's going on.
For another, the crystal has defects. A defect is a kind of impurity, and similarly interferes with the progress of the electron.
And finally, when a positive ion vibrates, it moves from it's ideal equilibrium position. This, too, is a "defect" of sorts, and can "stop" (or deflect) the electron.
So we have a picture or metaphor (and it's just that ... a picture or metaphor not to be taken too seriously) of electrons stopping and starting, and zig-zagging through the metal.
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$\begingroup$ Ok so you are saying that electrons can have any motion may be zig zag or any?? It depend on how electron collide with positive lattice but what about another questions.!! Why positive lattice oscillate about a mean position and why it cannot go to the positive terminal of the battery. $\endgroup$– SAHILCommented May 6, 2018 at 7:03
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$\begingroup$ Concerning zig-zag motion: yes, that's what I'm saying, but please don't forget that our best description of all this is in the language of quantum mechanics, where electrons are not particles (in the ordinary usage of the word) nor waves, but something completely different. Our mental pictures are only aids to help understand something that is outside of our normal comprehension. The positive ions oscillate because they have thermal energy. The chemical bonds are like springs. $\endgroup$– garypCommented May 6, 2018 at 14:18
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$\begingroup$ The electric fields in the bonds between positive ions is much greater than the fields that are applied by the battery. The fields produced by the battery are not strong enough to overcome the fields (and quantum mechanical forces) within the bond. The positive ions very rarely move. $\endgroup$– garypCommented May 6, 2018 at 14:20