Capacitance Questions: Troubleshooting Parallel Plate Capacitors

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Discussion Overview

The discussion revolves around troubleshooting issues related to measuring capacitance in parallel plate capacitors using a specific device (ams pcap02). Participants explore the behavior of the device when measuring capacitance, particularly in relation to grounding and the effects of external influences on readings.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant describes their setup and the unexpected behavior of the capacitance readings, noting that disconnecting the ground makes the device sensitive to external influences.
  • Another participant suggests measuring known capacitors to verify the device's functionality and checking for possible short circuits between terminals.
  • Several participants discuss the expected capacitance values based on the area and spacing of the plates, questioning whether the readings indicate an open circuit or very low capacitance.
  • There are mentions of parasitic capacitance affecting measurements, particularly when dealing with very low capacitance values.
  • One participant emphasizes the importance of connection layout and the potential for stray capacitance to influence readings.
  • Discussion includes the resolution limits of the measuring device and the implications of trying to measure capacitance below its resolution capability.
  • Participants express curiosity about the cost and applications of the pcap devices, noting their popularity and potential for home electronics labs.

Areas of Agreement / Disagreement

Participants express various viewpoints on the issues encountered, with no consensus reached on the underlying causes of the measurement discrepancies. Multiple competing explanations for the observed behavior remain, including the effects of parasitic capacitance and the limitations of the measuring device.

Contextual Notes

Limitations include potential missing assumptions regarding the setup, dependence on the specific device's characteristics, and unresolved questions about the connection layout affecting measurements.

  • #31
sysprog said:
we say that the speed of light is 1 something?.
In the 'natural system', c would to be dimensionless. The resulting values of distance and time would have suitably adjusted units so that the ratio would be 1. Once you choose the second (say, the units of distance would end up as 3e8 m so that c would measure as 1. (Other combinations are available)
 
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  • #32
sysprog said:
Please remember that 2019 is the year in which they/we screwed around with the units by assigning the speed of light/causation to be 1 -- oh and yeah, that speed is still somewhere around 286,000 miles per second -- where does that information go when we say that the speed of light is 1 something?.
WOW! Someone really screwed around with something since the last I knew the speed of light in a vacuum was 186,282 miles per second.
 
  • #33
sysprog said:
that speed is still somewhere around 286,000 miles per second
I guess the mile can be defined in terms of the distance traveled by light in 1s but I think it is actually defined as 1,609.344 metres. The last time I used the 186k miles per second value in anger was in secondary School in the early 60s. The mile is a quaint unit but we still use it (UK) when driving around but the fuel consumption figures for new cars don't mention miles. I let the car information display tell me the mpg but does anyone really believe that?
 
  • #34
Averagesupernova said:
WOW! Someone really screwed around with something since the last I knew the speed of light in a vacuum was 186,282 miles per second.
You're right -- my mistake.
sophiecentaur said:
I guess the mile can be defined in terms of the distance traveled by light in 1s but I think it is actually defined as 1,609.344 metres. The last time I used the 186k miles per second value in anger was in secondary School in the early 60s. The mile is a quaint unit but we still use it (UK) when driving around but the fuel consumption figures for new cars don't mention miles. I let the car information display tell me the mpg but does anyone really believe that?
When I was in school the mile was defined as 5280 feet.
 
  • #35
sysprog said:
When I was in school the mile was defined as 5280 feet.
Not "defined" in the strict sense - there are ratios between all length measurements. In the end, you need to start with one single length - in this case, afaik, the metre is the prime unit of length and it is defined in terms of the second and c. All the others follow that.
 
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