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I like to have an intuitive grasp of whats happening our tutor said they 'resist' the flow of electrons but I want to understand exactly whats happening.

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What's the effect of a resistor? It's a component that dissipates energy end thus lowers the voltage.

So what is voltage? It's the strength of the field that moves the electrons, while current represents the number of electrons flowing through the wire. Free electrons can be stopped all together or slowed all together, but it's not possible to select only some electrons to be stopped. They all feel the same field.

There is another reason why it's not possible, or at least practical, to lower the number of electrons. In this case the "resistor" should take away the particles from the flow and store them somewhere, for example by binding them on atoms. You can see the major problem here: in little time the resistor would be completely full and will stop working. Ejecting the electrons appears to be a solution, but that would interfere with the rest of the circuit and I don't think the general public would feel very excited about resistors that behave like $\beta$-emitting radioactive nuclei. ;)

I hope the answer is clear enough.

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    $\begingroup$ voltage and field strength are two different things $\endgroup$ – Azad May 12 '15 at 3:46
  • $\begingroup$ Yes, I used the wrong words. But then the strength of the field is measured in V/m, so the two quantities are proportional. What I wanted to say is that voltage defines the speed of the electrons, while current defines the number. $\endgroup$ – GRB May 12 '15 at 8:44
  • $\begingroup$ what does it mean to dissipate the energy? dissipate means to scatter, are you saying the electrons scatter through out the the resister and because of this less electrons come out the other side? $\endgroup$ – Ray Kay May 13 '15 at 11:10
  • $\begingroup$ No, the number of electrons entering the resistor is the same number of electrons exiting it. I'm saying that the resistor absorbs part of the energy of every electron, slowing them down, and dissipates it. A simple resistor dissipates energy by getting hotter, while a more complex kind of "resistor", like a lamp or a motor, may dissipate the energy by emitting light or by moving something. $\endgroup$ – GRB May 13 '15 at 12:15

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