Register to reply

Struggling with RC circuit concepts

Share this thread:
cjurban
#1
Mar4-13, 01:27 PM
P: 7
So we're covering RC circuits in my physics class and I'm having some trouble with the concepts.
When you have a circuit with a resistor and a battery, current passing through the resistor produces a voltage drop. If the battery is zero for our potential, the battery imbues the circuit with some potential difference which creates a current. My book says that the resistor will suck all of the potential energy out of the charges passing through it, since the voltage drop through the resistor equals the voltage of the battery. I don't understand how this could be, because if the charges in the wire have no potential energy after they've passed through the resistor how could they continue to be drawn toward the other end of the battery?
Also, what happens as charge flows through a wire attached to both terminals of a battery, with no other circuit components, if we assume the resistance to be "negligible?" According to V=IR, the voltage would go to zero! I remember reading that this is mostly an experimental law, and is only valid at certain temperatures in certain substances, but this is still a confusing point. Could someone help me clarify?
Phys.Org News Partner Physics news on Phys.org
Physicists discuss quantum pigeonhole principle
First in-situ images of void collapse in explosives
The first supercomputer simulations of 'spin?orbit' forces between neutrons and protons in an atomic nucleus
milesyoung
#2
Mar4-13, 03:00 PM
P: 428
... how could they continue to be drawn toward the other end of the battery?
I assume this is an ideal case where the resistor is connected to the battery terminals with ideal wires. This effectively means you should view the wires as an extension of the battery terminals (they're the same node) and as charge passes through the resistor, it simply passes between battery terminals.

Also, what happens as charge flows through a wire attached to both terminals of a battery ...
Ideal wire again? In that case, charge won't flow as the terminals of the battery are the same node and there can be no voltage between them.
cjurban
#3
Mar4-13, 04:47 PM
P: 7
that was my exact problem, I was struggling with the ideal wire concept! thanks so much :)

Ratch
#4
Mar5-13, 12:27 AM
P: 315
Struggling with RC circuit concepts

cjurban,

If the battery is zero for our potential, the battery imbues the circuit with some potential difference which creates a current.
If a battery puts out zero volts, then it is dead and no current exists.

My book says that the resistor will suck all of the potential energy out of the charges passing through it, since the voltage drop through the resistor equals the voltage of the battery.
Of course. If you make a battery supply a current continuously, eventually it will deenergize.

I don't understand how this could be, because if the charges in the wire have no potential energy after they've passed through the resistor how could they continue to be drawn toward the other end of the battery?
Voltage is the electrical density of the charge (joules/coulomb). If the energy density at one point is more (higher voltage) than the energy density (lower voltage) at another point, then the charge will flow to the lower energy density provided there is a conduction path.

Also, what happens as charge flows through a wire attached to both terminals of a battery, with no other circuit components, if we assume the resistance to be "negligible?" According to V=IR, the voltage would go to zero!
You would have an infinity of current across a infinitesimal amount of resistance. That cannot happen in the "real" world. It is like asking the question of what happens when a unstoppable force encounters an immovable wall. It is more a philosophical question than a scientific one.

Ratch
Naty1
#5
Mar6-13, 10:22 AM
P: 5,632
When you have a circuit with a resistor and a battery, current passing through the resistor produces a voltage drop. If the battery is zero for our potential, the battery imbues the circuit with some potential difference which creates a current.
If the battery dead, zero voltage across it's terminals, no current flows.



My book says that the resistor will suck all of the potential energy out of the charges passing through it, since the voltage drop through the resistor equals the voltage of the battery. I don't understand how this could be, because if the charges in the wire have no potential energy after they've passed through the resistor how could they continue to be drawn toward the other end of the battery?
The potential [voltage] energy is converted to heat energy in the resistor. electrons moving through the resistor continue to have potential energy and this moves them along the circuit and well as those ahead of them.


Also, what happens as charge flows through a wire attached to both terminals of a battery, with no other circuit components, if we assume the resistance to be "negligible?" According to V=IR, the voltage would go to zero!
In practice what happens, is that for a short time [no pun intended] a large current will flow until the potential energy of the ions [charge carriers] in the battery are depleted....the chemical energy in the battery is dissipated. The initial flow of current is determined by the resistance of the wire between the battery terminals....and as it gets hot, it's resistance typically increases....


Register to reply

Related Discussions
Venn Diagrams Concepts(including advanced concepts) Set Theory, Logic, Probability, Statistics 7
Understanding Concepts as opposed to Memorizing concepts. Academic Guidance 44
Parallel/Series circuit theory/concepts.. Introductory Physics Homework 5
Incorporate another function into this problem C++ Introductory Physics Homework 1
Struggling on this one Calculus 1