induced charge seperation
charging by contact
charging by induction
i basically don't get the difference b/w the three
all help appreciated..
can some oen explain the following topics in detail to me so that the concept is clear...the book is confusing me...the topics are as follows
induced charge seperation
charging by contact
charging by induction
i basically don't get the difference b/w the three
all help appreciated..
induced charge seperation
charging by contact
charging by induction
i basically don't get the difference b/w the three
all help appreciated..
About induced charge separation:
You need to have an electrically conductive object A (such as a metal rod) and a second object B (this one doesn't have to be a conductor) that is already charged. Remember that the definition of "conductor" is that charges are free to move around in it. To be precise, the negatively charged electrons are free to move, but the positively charged protons are stuck where they are, inside the atomic nuclei. Also, remember that everything contains massive quantities of positive and negative electric charge ALL THE TIME, but usually the positive and negative quantities are exactly equal, so they cancel out and we never notice them.
Now if you bring the charged object B near to one end of the conductor A, then B will exert forces on the electrons (and also on the protons, but that doesn't matter right now, since they can't move anyway). If B is positively charged, it will attract the electrons, and so (since A is a conductor and therefore they are free to move), they crowd in close to B. But that leaves too few electrons on the end of A that is facing away from B, so that end of A ends up with a positive charge, because the protons now outnumber the electrons there. Likewise, the end of A that is near to B will be negatively charged, because the electrons outnumber the protons there. Of course, if B were negatively charged, the whole situation would be reversed, since B would not repel the electrons of A instead of attracting them, and so they would move as far away from B as they could get, and then the far end of A would be negative and the near end would be positive.
Notice that no electrons actually enter A from outside, and no electrons leave A. All that happens is that the electrons that were already in A are moved around and rearranged. Therefore, the total charge on A is still zero, since there are still equal numbers of electrons and protons overall. That also tells you something about the charges at the opposite ends of A: since the net charge of A is zero, these charges at the ends of A must be equal and opposite, so that they will add up to zero as they should.
Summary: In induced charge separation, B never touches A, the end of A that is far from B gets charged the same sign as B, and the end that is near B gets charged the opposite sign as B. No electrons enter or leave A, the total charge of A is still zero, and the charges on the two ends are equal and opposite.
About charging by contact:
This starts out looking just like induced charge separation, but instead of just holding B near A, you ACTUALLY TOUCH A with B. If B was positive, all those electrons that are crowded in close to B can now flow onto B, which they will do since the positive charge on B attracts them. Now take B away, so that it doesn't touch A any more. The electrons that have flowed onto B are now trapped there and can't get back to A, so A has lost some of its electrons. Since its protons now outnumber its electrons, A now has a positive charge, and since B has been removed, there is nothing pushing the electrons around any more, so the remaining electrons spread out evenly again, and A ends up being positively charged ALL OVER, not just on one end.
Likewise, if B had been negatively charged, then the end of A near B would be positive (because of induced charge separation), so when B touched A, this time the electrons from B would flow onto A, since they would be attracted by the positive charges there. Again, after you take B away, these extra electrons are trapped on A, so A now has more electrons than protons, so it is negatively charged, and this charge spreads all over A after B is removed.
Summary: In charging by contact, B does touch A, some charge moves between them, and after B is removed, A ends up with a NONZERO net charge, and this charge is the same sign as the charge on B, and it is spread all over A.
About charging by induction:
Again, this starts out looking like induced charge separation, but this time, instead of touching A with B, you just hold B near one end of A, and then touch the OTHER END of A with another uncharged conductor C. Now, if B is positively charged, then the far end of A (far from B I mean) will be positively charged, so when you touch C to the far end of A, electrons from C will be attracted to this positive charge and move into A. Then you take C away, and then take B away. Now the electrons that flowed from C into A are trapped there, so A is negatively charged. Because C lost the very same electrons that A gained, C is positively charged, and the charge on C is the same size as the charge on A, i.e. A and C have equal and opposite charges.
Notice that the order of your actions is important. You bring B near one end of A, then touch the other end of A with C, then take C away, then take B away. The first two actions you can do in either order, but the last two must be done in the order I said. That's because if you take B away first, then there is nothing pulling on the charges of A, so they will move back to their natural positions, and the charge from C will flow back into C. Then whey you take C away, it has already got its original charges back, so no charges are left trapped in A.
Once again, if B is negatively charged, the results are reversed. The far end of A will now be negative, and th electrons there will flow into C as soon as C touches A, because that way they can get even farther from B, which is repelling them in this case, since B is negative. The same warning about the order of actions applies here too. First bring B near A and touch the other end of A with C, then remove C, then remove B, exactly the same as in the other case.
Summary: In charging by induction, you need one charged object B and two conductors A and C. B pushes or pulls charges from C onto A "by remote control." B never touches A, and all the charges are transferred between A and C. A and C end up with equal and opposite charges, with C having the same sign as B, and A the opposite sign as B.
Overall summary:
Separation: nothing touches A, net charge of A is zero, ends oppositely charged
Contact: B touches A, net charge of A is same as B, charge spread all over A
Induction: C (not B) touches A, net charge on A is opposite of B, charge spread all over A.
Hope this helps!
--Stuart Anderson
You need to have an electrically conductive object A (such as a metal rod) and a second object B (this one doesn't have to be a conductor) that is already charged. Remember that the definition of "conductor" is that charges are free to move around in it. To be precise, the negatively charged electrons are free to move, but the positively charged protons are stuck where they are, inside the atomic nuclei. Also, remember that everything contains massive quantities of positive and negative electric charge ALL THE TIME, but usually the positive and negative quantities are exactly equal, so they cancel out and we never notice them.
Now if you bring the charged object B near to one end of the conductor A, then B will exert forces on the electrons (and also on the protons, but that doesn't matter right now, since they can't move anyway). If B is positively charged, it will attract the electrons, and so (since A is a conductor and therefore they are free to move), they crowd in close to B. But that leaves too few electrons on the end of A that is facing away from B, so that end of A ends up with a positive charge, because the protons now outnumber the electrons there. Likewise, the end of A that is near to B will be negatively charged, because the electrons outnumber the protons there. Of course, if B were negatively charged, the whole situation would be reversed, since B would not repel the electrons of A instead of attracting them, and so they would move as far away from B as they could get, and then the far end of A would be negative and the near end would be positive.
Notice that no electrons actually enter A from outside, and no electrons leave A. All that happens is that the electrons that were already in A are moved around and rearranged. Therefore, the total charge on A is still zero, since there are still equal numbers of electrons and protons overall. That also tells you something about the charges at the opposite ends of A: since the net charge of A is zero, these charges at the ends of A must be equal and opposite, so that they will add up to zero as they should.
Summary: In induced charge separation, B never touches A, the end of A that is far from B gets charged the same sign as B, and the end that is near B gets charged the opposite sign as B. No electrons enter or leave A, the total charge of A is still zero, and the charges on the two ends are equal and opposite.
About charging by contact:
This starts out looking just like induced charge separation, but instead of just holding B near A, you ACTUALLY TOUCH A with B. If B was positive, all those electrons that are crowded in close to B can now flow onto B, which they will do since the positive charge on B attracts them. Now take B away, so that it doesn't touch A any more. The electrons that have flowed onto B are now trapped there and can't get back to A, so A has lost some of its electrons. Since its protons now outnumber its electrons, A now has a positive charge, and since B has been removed, there is nothing pushing the electrons around any more, so the remaining electrons spread out evenly again, and A ends up being positively charged ALL OVER, not just on one end.
Likewise, if B had been negatively charged, then the end of A near B would be positive (because of induced charge separation), so when B touched A, this time the electrons from B would flow onto A, since they would be attracted by the positive charges there. Again, after you take B away, these extra electrons are trapped on A, so A now has more electrons than protons, so it is negatively charged, and this charge spreads all over A after B is removed.
Summary: In charging by contact, B does touch A, some charge moves between them, and after B is removed, A ends up with a NONZERO net charge, and this charge is the same sign as the charge on B, and it is spread all over A.
About charging by induction:
Again, this starts out looking like induced charge separation, but this time, instead of touching A with B, you just hold B near one end of A, and then touch the OTHER END of A with another uncharged conductor C. Now, if B is positively charged, then the far end of A (far from B I mean) will be positively charged, so when you touch C to the far end of A, electrons from C will be attracted to this positive charge and move into A. Then you take C away, and then take B away. Now the electrons that flowed from C into A are trapped there, so A is negatively charged. Because C lost the very same electrons that A gained, C is positively charged, and the charge on C is the same size as the charge on A, i.e. A and C have equal and opposite charges.
Notice that the order of your actions is important. You bring B near one end of A, then touch the other end of A with C, then take C away, then take B away. The first two actions you can do in either order, but the last two must be done in the order I said. That's because if you take B away first, then there is nothing pulling on the charges of A, so they will move back to their natural positions, and the charge from C will flow back into C. Then whey you take C away, it has already got its original charges back, so no charges are left trapped in A.
Once again, if B is negatively charged, the results are reversed. The far end of A will now be negative, and th electrons there will flow into C as soon as C touches A, because that way they can get even farther from B, which is repelling them in this case, since B is negative. The same warning about the order of actions applies here too. First bring B near A and touch the other end of A with C, then remove C, then remove B, exactly the same as in the other case.
Summary: In charging by induction, you need one charged object B and two conductors A and C. B pushes or pulls charges from C onto A "by remote control." B never touches A, and all the charges are transferred between A and C. A and C end up with equal and opposite charges, with C having the same sign as B, and A the opposite sign as B.
Overall summary:
Separation: nothing touches A, net charge of A is zero, ends oppositely charged
Contact: B touches A, net charge of A is same as B, charge spread all over A
Induction: C (not B) touches A, net charge on A is opposite of B, charge spread all over A.
Hope this helps!
--Stuart Anderson