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electric current and charge

What is this paragraph trying to say?

'An individual electron from a torch battery may not complete a single circuit (from battery to bulb to batter) before the battery goes flat. With such a slow speed of travel, some other factor must be involved if the bulb is lit as soon as a torch is switched on. Whether the electrons are travelling quickly or slowly in a circuit, the following relationship always holds: Charge in coulombs = current in amperes x time in seconds'
Reply 1
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joostan
13
Original post by tammie123
What is this paragraph trying to say?

'An individual electron from a torch battery may not complete a single circuit (from battery to bulb to batter) before the battery goes flat. With such a slow speed of travel, some other factor must be involved if the bulb is lit as soon as a torch is switched on. Whether the electrons are travelling quickly or slowly in a circuit, the following relationship always holds: Charge in coulombs = current in amperes x time in seconds'


It says that the drift velocity of electrons is very slow, and that the speed of electrons moving is not related to whether or not something will turn on (provided the electrons are moving at all)
And that Q=It in SI units.
Original post by joostan
It says that the drift velocity of electrons is very slow, and that the speed of electrons moving is not related to whether or not something will turn on (provided the electrons are moving at all)
And that Q=It in SI units.


So drift velocity can occur without a battery?
Reply 3
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joostan
13
Original post by tammie123
So drift velocity can occur without a battery?


If by battery you mean power supply:
No . . . I = nAvQ
Therefore you must have a current to have a drift velocity - you can't have a current without an e.m.f.
That does not mean that the electrons are not moving there is such a thing as r.m.s. Drift velocity is just a general trend of movement of electrons caused by a p.d. being applied.
Original post by joostan
If by battery you mean power supply:
No . . . I = nAvQ
Therefore you must have a current to have a drift velocity - you can't have a current without an e.m.f.
That does not mean that the electrons are not moving there is such a thing as r.m.s. Drift velocity is just a general trend of movement of electrons caused by a p.d. being applied.



Oh ok but then what do you mean by the bit below? When what is turned on?


Original post by joostan
the speed of electrons moving is not related to whether or not something will turn on.
Reply 5
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joostan
13
Original post by tammie123
Oh ok but then what do you mean by the bit below? When what is turned on?


Provided there is a drift velocity there can be a current. If there is a current the device in the circuit will be able to turn on - as the paragraph says.
Original post by joostan
Provided there is a drift velocity there can be a current. If there is a current the device in the circuit will be able to turn on - as the paragraph says.


Oh I get it, so as long as there is a current the bulb will light as electrons further down in the wire will reach it, despite the slow drift velocity. Am I right? Or have I misunderstood?
Reply 7
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joostan
13
Original post by tammie123
Oh I get it, so as long as there is a current the bulb will light as electrons further down in the wire will reach it, despite the slow drift velocity. Am I right? Or have I misunderstood?


You are correct. :smile:

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