Learn About Voltage, Current & Resistance

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Discussion Overview

The discussion revolves around the concepts of voltage, current, resistance, and internal resistance, including their definitions, relationships, and implications in electrical circuits. Participants explore both theoretical and practical aspects of these topics.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants seek basic definitions of voltage, current, resistance, and internal resistance.
  • Voltage is described as the potential difference between two points, while current is characterized as the rate of change of charge with time.
  • Resistance is noted to be proportional to voltage and inversely proportional to current.
  • Internal resistance is defined as the Thevenin resistance seen by an external source.
  • Analogies involving water flow are used to illustrate the relationships between voltage, current, resistance, and internal resistance.
  • Questions arise regarding the relationship between internal resistance and electromotive force (EMF), with references to Ohm's law.
  • Some participants discuss the implications of internal resistance in circuits and its effect on overall resistance and current flow.
  • Concerns are raised about the dangers of high resistance in circuits and the energy dissipation associated with it.
  • Participants explore the possibility of achieving zero internal resistance in electrical devices, with some asserting that it is impossible.

Areas of Agreement / Disagreement

Participants express a range of views on the definitions and implications of internal resistance, with some agreeing on its effects in circuits while others question the feasibility of achieving zero internal resistance in electrical devices. The discussion remains unresolved on several points, particularly regarding the nuances of internal resistance and its practical implications.

Contextual Notes

Some definitions and relationships presented depend on specific conditions or assumptions, such as the context of circuit design and the characteristics of materials used.

Air
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Can I have some information about these topics?

  • Voltage
  • Current
  • Resistance
  • Internal Resistance

Thank You in Advance. o:)
 
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You need to be a little more specific.
 
Questions that general/vague will at best get you a reference to google or a wik link. You'll need to be more specific if you want some actual answers.
 
Voltage = potential difference between two points
Current = rate of change of charge with time
Resistance = proportional to the voltage and inversely proportional to current
Internal Resistance = Thevenin resistance seen by outside source
 
Mindscrape said:
Voltage = potential difference between two points
Current = rate of change of charge with time
Resistance = proportional to the voltage and inversely proportional to current
Internal Resistance = Thevenin resistance seen by outside source

Thank You. I needed information like this. :smile:
 
What is Internal Resistance in relation to EMF?
 
Think of it analogous to water flowing from an elevated tank through a small hose.

Voltage is the pressure behind the water which corresponds to amount of water in the tank pushing down.

Current is the speed of the water.

Resistance is something in the hose obstructing the path of water flow.

Internal resistance is the resistance of the water having friction with pipe walls.
 
Agnostic said:
Think of it analogous to water flowing from an elevated tank through a small hose.

Voltage is the pressure behind the water which corresponds to amount of water in the tank pushing down.

Current is the speed of the water.

Resistance is something in the hose obstructing the path of water flow.

Internal resistance is the resistance of the water having friction with pipe walls.

Thats a very good analogy. Thanks. :smile:

______________________________________________________

Can someone answer this question:

What is Internal Resistance in relation to EMF?
 
  • #10
What do you mean by internal resistance?
Do you disagree with Mindscrape's definition?

E=IR
 
  • #11
Anived said:
What is Internal Resistance in relation to EMF?

Well, if you have a given EMF, generated by a magnetic field changing in time, and are near some circuit or wire, you can just use good ol' ohms law to find the resistance:

V=IR, or using different notation for your EMF, EMF=IR, or R=EMF/I, so the reistance in the circuit is proportional to the strength of the EMF, and inversely proportional to current.
 
  • #12
NoTime said:
What do you mean by internal resistance?
Do you disagree with Mindscrape's definition?

E=IR

The Voltage that is lost in the Power supply.
 
  • #13
Usually, for most things, it's negligable.
For actively regulated power supplys it can be 0 or even negative.

If it is a factor, then the power supply resistance gets added to the rest of the resistance in the circuit.
 
  • #14
NoTime said:
Usually, for most things, it's negligable.
For actively regulated power supplys it can be 0 or even negative.

If it is a factor, then the power supply resistance gets added to the rest of the resistance in the circuit.

Does this affect the circuit in any way?
 
  • #15
Anived said:
Does this affect the circuit in any way?
Yes, in exactly the same way a normal resistor would. Suppose you have a cell with a 12V emf and 1[itex]\Omega[/itex] internal resistance. This would be equivalent to a circuit containing a 12V cell with no internal resistance, in series with a 1[itex]\Omega[/itex] resistor.
 
  • #16
Hootenanny said:
Yes, in exactly the same way a normal resistor would. Suppose you have a cell with a 12V emf and 1[itex]\Omega[/itex] internal resistance. This would be equivalent to a circuit containing a 12V cell with no internal resistance, in series with a 1[itex]\Omega[/itex] resistor.

I see.

Is it dangerous if the resistance gets high? If so why and what happens?
 
  • #17
Anived said:
I see.

Is it dangerous if the resistance gets high? If so why and what happens?

Resistors dissipate energy, how do you suggest they do this?
 
  • #18
Hootenanny said:
Resistors dissipate energy, how do you suggest they do this?

Resistance serves to limit the amount of Current through the circuit with a given amount of Voltage supplied by the battery.
 
  • #19
Anived said:
Resistance serves to limit the amount of Current through the circuit with a given amount of Voltage supplied by the battery.
Yes, it does this by dissipating (removing) energy (from the circuit). This energy is dissipated as heat. Therefore, if you have a high resistance together with a high current flow, then large amounts of heat will be dissipated.
 
  • #20
Hootenanny said:
Yes, it does this by dissipating (removing) energy (from the circuit). This energy is dissipated as heat. Therefore, if you have a high resistance together with a high current flow, then large amounts of heat will be dissipated.

After lots of heat is dissipated, does the Resistance, Voltage or Current change (i.e go lower or higher)?

I thank all the people who have helped me so far. You have increased my knowledge. :smile:
 
  • #21
As the temperature of a conductor increases, the resistance of that conductor also increases (note that a resistor is a conductor). Therefore, we have an example of positive feedback in a resistor; the resistance causes an increase in temperature of the resistor. This in turn increases the resistance of the resistor, thus further increasing the resistance. Therefore, the resistance of the resistor will increase.
 
  • #22
Is it possible to have an electrical product that has Zero Internal Resistance?
 
  • #23
Anived said:
Is it possible to have an electrical product that has Zero Internal Resistance?
Some materials are superconductors, i.e. at low temperature have a zero resistance, if that is what you mean.
 
  • #24
Hootenanny said:
Some materials are superconductors, i.e. at low temperature have a zero resistance, if that is what you mean.

No I mean the Internal Resistance which is The Resistance within a voltage source, such as an Electric Cell or Generator.

So...Can a Electric Cell be made so that it has no Internal Resistance or is it impossible?

(If you do not understand my question then please ignore it. :smile:)​
 
  • #25
No, it is not possible to create any electrical device (cell, battery, generator) with a zero internal resistance. However, in some cases where the load resistance is large compared to the internal resistance, it is possible to ignore the internal resistance.
 

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