The true meaning of voltage drop

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Discussion Overview

The discussion revolves around the concept of voltage drop in circuits, particularly in the context of CE amplifiers with negative feedback. Participants explore the physical interpretation of voltage drop, the relationship between current and voltage across resistors, and the implications of feedback mechanisms in transistor circuits.

Discussion Character

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

Main Points Raised

  • One participant expresses confusion about the physical meaning of the emitter becoming more positive in CE amplifiers as hfe increases, questioning how this relates to charge and potential difference.
  • Another participant seeks clarification on the role of negative feedback in the circuit and its effects on emitter voltage.
  • Some participants discuss the relationship between emitter current and the voltage drop across the emitter resistor, with one noting that increased current leads to a larger voltage drop.
  • There is a suggestion that thinking in terms of electrons may not be helpful, and using transistor equivalent circuits could provide clarity.
  • One participant argues that voltage drop is a loss of potential energy in resistors, while another challenges the notion that current can cause voltage, emphasizing that voltage is the driving force for current flow.
  • A later reply clarifies that voltage drop is a measurable physical quantity, but its interpretation can lead to confusion regarding the relationship between current and voltage in resistors.

Areas of Agreement / Disagreement

Participants express differing views on the nature of voltage drop and its physical interpretation. While some agree that voltage drop is a measurable quantity, others debate the causal relationship between current and voltage, indicating that the discussion remains unresolved.

Contextual Notes

Limitations in understanding arise from the complexity of the concepts discussed, including the assumptions about current and voltage relationships in resistors and the effects of feedback in transistor circuits.

Who May Find This Useful

This discussion may be of interest to those studying electronics, particularly in understanding the nuances of voltage drop, feedback mechanisms in amplifiers, and the physical principles underlying circuit behavior.

  • #31
jim hardy said:
So hydraulic analogy is useful to get your brain accustomed to working circuits "in your head" .
old jim

Yes - I fully agree.
As an interesting exercise, one could try to explain the amplifying properties of a transistor using the hydraulic analogy - in particular, if it seems to be possible that a tiny flow of water is able to control (with gain !) the water flow of a much larger river.
 
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  • #32
LvW said:
if it seems to be possible that a tiny flow of water is able to control (with gain !) the water flow of a much larger river.
Pressure actuated valve on a much larger flow pipe? (Ah, this would be a FET)
 
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  • #33
Voltage is work done per unit charge , therefore when we say voltage drop work is done between the resistor ie really a energy loss ,and it is physical quantity
 
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  • #34
You have to be careful using purely conceptual thinking with physics. Sometimes things behave in a way that's not intuitive. On the the other hand, the math does not always clarify dependencies such as the fact voltage has to be present before current will flow. Usually you need to understand the math first to understand the behavior conceptually. We use the term Voltage drop in a practical catch all manner, but the term fails to provide a sense of what's really going on there. The outward appearance is a voltage differential between one node and another, but there's physical behaviors taken for granted that result in those observable measurements.
 
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  • #35
CraigHB said:
We use the term Voltage drop in a practical catch all manner, but the term fails to provide a sense of what's really going on there.

"Voltage drop" is almost slang for voltage across something that is removing energy from a circuit, ie a load such as a motor or lamp
curiously
it's rare to hear the converse term "Voltage rise" describing voltage across something that deposits energy ie a source such as a battery or power supply.
 
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  • #36
Thanks everyone, your help is very helpful!
 

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