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Current electricity

by FizixFreak
Tags: current, resistance, series combination
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FizixFreak
#1
Mar7-10, 04:52 AM
P: 188
why is current always same for series resistances i mean if a current passes through a resistor a then same current will pass through resistor b does the first resistor not reduces current
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berkeman
#2
Mar7-10, 06:03 AM
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Quote Quote by FizixFreak View Post
why is current always same for series resistances i mean if a current passes through a resistor a then same current will pass through resistor b does the first resistor not reduces current
Current is continuous through a loop conductor (at least for a DC current or an AC current where the loop size is much smaller than a wavelength). Think of it as beeds on a string being pulled/pushed through a pipe...
Pythagorean
#3
Mar7-10, 06:04 AM
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Current is the flow of electrons, voltage tells us something about the force on the electrons.

The flow through the whole series is affected by both resistors all at once. The voltage drops with each resister in series.

FizixFreak
#4
Mar7-10, 10:11 AM
P: 188
Current electricity

Quote Quote by berkeman View Post
Current is continuous through a loop conductor (at least for a DC current or an AC current where the loop size is much smaller than a wavelength). Think of it as beeds on a string being pulled/pushed through a pipe...
i m not quite catching up here can you please elaborate
vin300
#5
Mar7-10, 10:22 AM
P: 512
If the current in series combination isn't same everywhere, there'd be accumulation of free electrons at some place and the wire would go on charging up, but the wire must be electrically neutral, and there's no good reason for this not to be true unless in relative motion
Studiot
#6
Mar7-10, 11:40 AM
P: 5,462
I think this is a perfectly reasonable query for a beginner to make.

This is where the hydraulic analogy is appropriate (please don't spoil this thread with discussion other failings of this analogy)

Imagine that your series resistors are like pipes, one after the other.

If you keep pumping water into one end it has to come out of the other or burst the pipes. Of course the longer the pipes the harder you have to pump to push the water through.

Resistors are like this, if you push current into one end it has to come out of the other.
Of course the is something which is lost in passing the resistor. This is the voltage. The greater the resistance the greater the voltage loss.
Buckethead
#7
Mar7-10, 01:09 PM
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Quote Quote by FizixFreak View Post
why is current always same for series resistances i mean if a current passes through a resistor a then same current will pass through resistor b does the first resistor not reduces current
Yes it does because the voltage across b is now less. Using I=E/R, if the resistance increases (by adding the second resistor), then the current will drop.
FizixFreak
#8
Mar8-10, 12:56 PM
P: 188
Quote Quote by Studiot View Post
I think this is a perfectly reasonable query for a beginner to make.

This is where the hydraulic analogy is appropriate (please don't spoil this thread with discussion other failings of this analogy)

Imagine that your series resistors are like pipes, one after the other.

If you keep pumping water into one end it has to come out of the other or burst the pipes. Of course the longer the pipes the harder you have to pump to push the water through.

Resistors are like this, if you push current into one end it has to come out of the other.
Of course the is something which is lost in passing the resistor. This is the voltage. The greater the resistance the greater the voltage loss.
okay so i think i got it according to the analogy as the water moves through a pipe with a small diameter that pipe will be considered to offer higher resistance but the same amount of water will flow through the pipe just as it will pass through a pipe of larger diameter right????
Studiot
#9
Mar8-10, 02:45 PM
P: 5,462
I deliberately didn't mention the pipe diameter, I said longer.

But yes a smaller diameter pipe offers greater resistance to flow than a larger one so you have to pump harder to push the flow through.

Buckethead had a slightly different interpretation of you post and thinking about it he might have been right.

I though you meant putting one resistor after another (hence my comment about pipes).
This is called a series circuit and since there is only one path available all the current that flows into the first resistor , flows out and into the second one and so on, like water in the pipes.

Alternatively if you meant that you have one resistor connected to a supply (battey etc) and you change it for a different one will you get a different current, the answer is yes. The battery voltage will not change (within reason) but the current depends upon the total resistance seen by the battery.
FizixFreak
#10
Apr29-10, 12:35 AM
P: 188
Quote Quote by Studiot View Post
I deliberately didn't mention the pipe diameter, I said longer.

But yes a smaller diameter pipe offers greater resistance to flow than a larger one so you have to pump harder to push the flow through.

Buckethead had a slightly different interpretation of you post and thinking about it he might have been right.

I though you meant putting one resistor after another (hence my comment about pipes).
This is called a series circuit and since there is only one path available all the current that flows into the first resistor , flows out and into the second one and so on, like water in the pipes.

Alternatively if you meant that you have one resistor connected to a supply (battey etc) and you change it for a different one will you get a different current, the answer is yes. The battery voltage will not change (within reason) but the current depends upon the total resistance seen by the battery.
let say i have two resistances in parallel arrangment of the same value now when the circuit is established will the currents through both be the same as the resistances have the same value ???
russ_watters
#11
Apr29-10, 05:36 AM
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Yes.
FizixFreak
#12
Apr30-10, 05:41 AM
P: 188
Quote Quote by russ_watters View Post
Yes.
how do the resistors decrease the potential of the charges in a current loop i mean hoe do these resistors work??????
Born2bwire
#13
Apr30-10, 06:50 AM
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Quote Quote by FizixFreak View Post
how do the resistors decrease the potential of the charges in a current loop i mean hoe do these resistors work??????
The electrons bump into the materials that make up the resistor. Each collision leeches off energy from the electrons and transfers it as a vibration to the resistor's atomic lattice. This vibration is heat. So the resistors convert the kinetic energy of the electrons to heat via collisions. This is known as the Drude model if you would like to look it up.


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