0
$\begingroup$

So I have this question in my textbook and Ive also got it in my test. Ive written a wrong answer. My friend wrote the drift velocities of each particle add up and he got full marks. Is it right? Can you please explain. I have checked this answer elsewhere but they use terms such electromagnetic waves which is not yet thought to us. Could you please explain in simple terms? Ok, this is the edited question. This was the answer of my teacher: $I=neAv_d$. Although $v_d$ is very small but $n$ the number density of electrons is very very large as compared to the drift velocity hence although the velocity of the electrons is very small to get to the other end instantly but they are so large in number that the current is established immediately. Is this the right definition?

$\endgroup$
  • 1
    $\begingroup$ Each electron pushes the next one! $\endgroup$ – lucas Jun 24 '16 at 13:47
  • 1
    $\begingroup$ your friend got marks for free.The velocities don't add up $\endgroup$ – Kishan Kumar Jun 24 '16 at 14:55
4
$\begingroup$

It is like water in a hose. If the hose is full of water, water flows out the end immediately when you turn on the faucet. A drop of water at the faucet pushes a drop next to it, which pushes the next drop.

Water doesn't flow that fast. If the hose is empty, it takes a while to reach the end.

| cite | improve this answer | |
$\endgroup$
  • $\begingroup$ Could you please answer with physics terms. One which could be presented in my exam if asked again. $\endgroup$ – Sreekara Yachamaneni Jun 24 '16 at 13:57
  • $\begingroup$ Sorry. See our policy on homework questions. But it sounds like your friend got credit for an incorrect answer. $\endgroup$ – mmesser314 Jun 24 '16 at 14:07
  • $\begingroup$ '@Sreekara I think the answer by @lucas has sufficient physics terms. $\endgroup$ – hsinghal Jun 24 '16 at 17:17
  • $\begingroup$ @Sreekara: This is an intuitive explanation, and since you wanted simple terms I agree with it. Another explanation would be that the electrons in the metal form a gas because they are free to move. The speed of sound in that gas is close to but somewhat less than the speed of light, and that is the speed at which differences in voltage (i.e. signals) can travel. If current were not established immediately, that would mean electrons were concentrated in one place, therefore would have higher pressure (voltage) there, which would be quickly dissipated with current. $\endgroup$ – Mike Dunlavey Jun 24 '16 at 17:35
-2
$\begingroup$

Man you need to understand that there are large no of electrons present inside a conductor where one electron pushes the other by a velocity known as drift velocity when an external field is applied as a result these velocities add up and thus increasing the no of electrons passing through a given cross sectional area .Thus we presume that though the drift velocity of individual electron is less but current is established immediately.

| cite | improve this answer | |
$\endgroup$
  • 1
    $\begingroup$ "One electron pushes the other by a velocity", What does this even mean ? $\endgroup$ – Mitchell Jul 8 '17 at 17:46

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.