Is the term loop loosely defined in Faraday's law?

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Discussion Overview

The discussion revolves around the definition and implications of the term "loop" in Faraday's law, particularly in the context of induced voltage in open versus closed loops. Participants explore the conditions under which voltage is induced and the conceptual challenges that arise from the definition of a loop.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • One participant questions whether a "loop" must be closed for voltage to be induced, expressing confusion about the implications of an open-ended voice coil.
  • Another participant asserts that voltage and current can still be induced even if the loop is not closed, noting that the oscilloscope's high input impedance makes it similar to an open loop.
  • A further explanation suggests that voltage is defined along a specific path in a closed loop, emphasizing the importance of starting and ending at the same point to determine voltage around that path.
  • There is mention of practical applications involving microphones, indicating that certain types of microphones may still produce an output even when the loop is not closed, depending on the microphone design.

Areas of Agreement / Disagreement

Participants express differing views on whether a loop must be closed for voltage induction, with some arguing that it is not necessary while others emphasize the significance of a closed loop for defining voltage along a path. The discussion remains unresolved regarding the implications of an open loop in the context of Faraday's law.

Contextual Notes

Participants highlight the dependency on definitions of "loop" and the conditions under which voltage is measured, indicating that assumptions about the nature of the loop may affect the understanding of induced voltage.

LightFantastic
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Is the term "loop" loosely defined in Faraday's law?

A voltage will be induced in a loop of wire when the magnetic field flux through the loop changes

If you're reading this, you probably know what happens when you hook up the leads from an oscilloscope to a microphone. Nothing, lol. There needs to be relative motion between the voicecoil and the permanent magnet for you to view any voltage fluctuations.And here is the origin of my confusion,

Disconnect the leads. The voicecoil is now open ended. In other words, it is NO LONGER a true loop. Will a voltage still be induced? Also, voltage is a measure between two points or ends in the case of a voice coil. How am I supposed to find the "ends" in a circle?
 
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You mean - does the loop have to be closed?
No.
 
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Without the loop closed there will be a voltage and current induced in the loop. By the way, the scope is a very high input impedance and having it connected is very close to having the loop open. With the loop closed, the voltage around the loop gets smaller and the current gets bigger. The voltage around the loop is defined for a specific path. If we start at point A, go around the loop once and end on the same point, there is a definite voltage along that path.

Claude
 
LightFantastic said:
A voltage will be induced in a loop of wire when the magnetic field flux through the loop changes

If you're reading this, you probably know what happens when you hook up the leads from an oscilloscope to a microphone. Nothing, lol. There needs to be relative motion between the voicecoil and the permanent magnet for you to view any voltage fluctuations.And here is the origin of my confusion,

Disconnect the leads. The voicecoil is now open ended. In other words, it is NO LONGER a true loop. Will a voltage still be induced? Also, voltage is a measure between two points or ends in the case of a voice coil. How am I supposed to find the "ends" in a circle?

Using a moving coil "dynamic" microphone, you should get an output if you talk into it and this may be visible on the oscilloscope trace if you have enough gain in the oscilloscope.

These microphones are now fairly rare and you might be using an "electret" microphone which requires a source of DC voltage to make it work.
 

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