# resistors

#### curious_to_know

Joined Jun 23, 2007
9
any experienced peson here???? WHAT ROLE DOES THE RESISTOR PLAY WHEN THE CURRENT IN THE WHOLE CIRCUIT REWMAINS THE SAME? ( i mean.. that the resistor is supposed to oppose the flow of current. But if this is the case there should be some change in the current like slowing it down or something, which does not happen? right? so what role is the resistor playing after all?)

#### Salgat

Joined Dec 23, 2006
221
Uh, I guess what you are asking is what if a current supply was put through a circuit and what role does the resistor play? I guess it would determine the voltage.

#### recca02

Joined Apr 2, 2007
1,214
consume power needlesly, i guess.
can u be a little more specefic?
resistor in parallel will shunt the current.

#### Dave

Joined Nov 17, 2003
6,970
Uh, I guess what you are asking is what if a current supply was put through a circuit and what role does the resistor play? I guess it would determine the voltage.
I concur with Salgat simply by Ohm's Law: V = IR - for constant I, as R increases so does V.

consume power needlesly, i guess.
And that would be the net result of increasing R.

Dave

#### recca02

Joined Apr 2, 2007
1,214
i m a bit confused abt it determining the voltage though,
of course v=ir but since current is constant any device u connect in the circuit (in series) will always have the same voltage drop as current is supposed to be same (in this case).
for a resistor connected in parallel that shud work.

#### Dave

Joined Nov 17, 2003
6,970
Determination of the voltage is probably the wrong word. Given the information in the OP one must assume we have a single resistor and a voltage source that is variable sufficient to maintain a constant voltage. Therefore, changes in the resistor will be reflected in the voltage to maintain constant current.

Perhaps the OP could give us a circuit with which to explain specifically to that application.

Dave

#### curious_to_know

Joined Jun 23, 2007
9
WHAT ROLE DOES THE RESISTOR PLAY WHEN THE CURRENT IN THE WHOLE CIRCUIT REWMAINS THE SAME? ( i mean.. that the resistor is supposed to oppose the flow of current. But if this is the case there should be some change in the current like slowing it down or something, which does not happen? right? so what role is the resistor playing after all?)

#### recca02

Joined Apr 2, 2007
1,214
the role of resistor remains the same, that is to oppose the current.
the confusion that i think u have is due to constant current source.
before further discussion may i suggest u to read abt current sources from wiki.
if you take into account the large voltage in series with large resistance to act as constant current source the role of resistor is the same but but because of its relatively small value the change in current is insignificant.

#### Dave

Joined Nov 17, 2003
6,970
WHAT ROLE DOES THE RESISTOR PLAY WHEN THE CURRENT IN THE WHOLE CIRCUIT REWMAINS THE SAME? ( i mean.. that the resistor is supposed to oppose the flow of current. But if this is the case there should be some change in the current like slowing it down or something, which does not happen? right? so what role is the resistor playing after all?)
All the resistor does is convert energy within the current into heat - in this function it is a current limiting component. For a constant voltage and resistance the current will remain the same (it does not change unless the voltage or resistance changes), otherwise you have a fundamental violation of Ohm's Law: V = IR - it is just as simple as this.

Dave

Joined Jul 4, 2007
2
WHAT ROLE DOES THE RESISTOR PLAY WHEN THE CURRENT IN THE WHOLE CIRCUIT REWMAINS THE SAME? ( i mean.. that the resistor is supposed to oppose the flow of current. But if this is the case there should be some change in the current like slowing it down or something, which does not happen?
For a series circuit, every electron that leaves (flows from) a power source (ie. battery) into on end of a conductor "pushes" an electron out of the conductor and back into the other end (terminal) of the power source.

A crude example...
Picture a hose full of marbles from end to end. Suppose that the marbles were equal in width to the diameter of the hose. They can not overtake eachother! So as you push one in... another must come out the other end, yes?

The point is that current flow stays the same in a series circuit. If you squeezed the hose a bit (to add resistance), not so tight that no marbles could move, but just tight enough so that it was harder (due to friction), then you could still see that one marble in causes one marble out?

I hope this helps. I am learning too!   #### thingmaker3

Joined May 16, 2005
5,084
WHAT ROLE DOES THE RESISTOR PLAY WHEN THE CURRENT IN THE WHOLE CIRCUIT REWMAINS THE SAME?
The resistor is what is keeping the current the same. Take out the resistor, you have an open circuit and current stops altogether. Short around the resistor, and current increases drastically. Leave the resistor alone, and current remains at I = E/R.

#### techroomt

Joined May 19, 2004
198
there are some circuit basics you must be familiar with. dc/ac power sources, serial, parallel, and ser/par circuits are all the study of Kirchoff's laws of voltage drops (how much voltage there is across a component) and currents. a resistor will drop voltage and therfore control the current. example: a 12vdc source (car battery) is connected to single 3 ohm load (heating element). 12v/3ohm = 4 amps of current. now, hypothetical install a 3 ohm resistor in between 12v battery and 3 ohm element (in series). the total resistance is now 3 ohm + 3 ohm = 6 ohm. 12v/6 ohm = 2 amps current. notice reduction of current. btw each 3 ohm load has 2 amps of current and is dropping 6 vdc each.