How Do You Calculate Magnetic Flux from a Nearby Spark?

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Discussion Overview

The discussion revolves around calculating the magnetic flux through a loop caused by a nearby spark. Participants explore the necessary parameters and information required to perform this calculation, including the characteristics of the spark and the medium through which it occurs.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant inquires about how to represent the current from a spark to calculate magnetic flux, noting the challenge of the spark's instantaneous nature and the need for additional information.
  • Another participant emphasizes the necessity of knowing the voltage between the spark source and its destination, questioning whether the spark occurs in air or another gas.
  • A participant provides a hypothetical scenario where the spark is 2m long in normal air, estimating an initial voltage of 1.94MV based on the breakdown voltage of air.
  • Further discussion raises the importance of knowing the duration of the spark to advance the calculation.
  • One participant suggests that additional information is needed, such as the energy of the spark, current, or resistance of the air at breakdown, to determine the current flowing through the spark.
  • Another participant proposes that if the duration of the spark is known (e.g., 0.1s), it could help in calculating the energy, power, and current, but emphasizes the need for the spark's energy to proceed.
  • Participants discuss various relationships between power, current, voltage, and energy, indicating multiple approaches to solving the problem depending on the available data.

Areas of Agreement / Disagreement

Participants generally agree that additional information is necessary to calculate the magnetic flux from the spark, particularly regarding the energy and current of the spark. However, there is no consensus on how to obtain this information or the best approach to take.

Contextual Notes

Limitations include the lack of specific values for energy, current, and resistance, as well as the dependence on the assumptions made about the spark's characteristics and the medium.

elegysix
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If I wanted to know how to find the magnetic flux through a loop, I'd need to know the current flowing near it. If that current is in the form of a spark, how do I represent that?

The spark is nearly instantaneous, and I've got no idea how to determine the number of charges which flowed within it...

essentially - I want to find the magnetic flux in a loop due to a spark nearby. I know that the breakdown of air is at .97MV/m... and suppose I know the length of the spark. where do I go from there? do i need more information?

any thoughts?

thanks!
 
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You haven't really given us anything to go on. We would need to know the voltage between the source of the spark and whatever it is going to. (If it's just a spark in the air then just the applied voltage to the source) Is the spark just in normal air or another type of gas?
 
lets say normal air with the breakdown at .97MV/m... say the spark is 2m long, that'd give us an initial V = 1.94MV
 
elegysix said:
lets say normal air with the breakdown at .97MV/m... say the spark is 2m long, that'd give us an initial V = 1.94MV

Alright. So how long does this spark last?
 
You need two more pieces of information to solve this problem; either:
-The energy of the spark,
-The current of the spark,
-Resistance of the air(at breakdown)
and
time/duration of spark
or energy

From any of those you would solve for current. The easiest to find would probably be to find energy. For a spark plug (example) you would simply find the energy stored in any capacitors and inductors, and that would give you the energy.

From there, realize that power is current times voltage, and that power is energy per unit time. That should get you started.
 
Suppose the flash lasts for .1s...
that gives us
V0=1.94MV
Length=2m
t=0.1s
... does this get us any further?
 
You still haven't given us anything that will let us know the energy. We need the energy of the spark to do this.

Once you have the spark energy:
P=I*V
P*T=E
I=E/(T*V)

Or if you have resistance:
V=IR
I=V/R

Also, if you know length then Vbreakdown=kbreakdown*r

If you have a desired current 'I' then you will have to provide P watts of power for a given spark IE:
P=Idesired*kbreakdown*r watts

If it's a short duration spark, then time will be determined by input Energy and resistivity of ionized air.
 
Last edited:

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