Why c is divided while converting cgs into SI system?

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  • Thread starter Thread starter RAFIQ MULLA
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    Cgs Si System
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Discussion Overview

The discussion revolves around the conversion of units from the centimeter-gram-second (cgs) system to the International System of Units (SI), specifically addressing the treatment of the speed of light (c) during this conversion process. Participants explore the implications of unit conversion and the mathematical relationships involved.

Discussion Character

  • Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant questions why c, the speed of light, is divided in the conversion process, suggesting a need for clarification on the specifics of the division.
  • Another participant expresses confusion, stating that there is typically no division of c in the conversion from cgs to SI, prompting a request for examples.
  • A third participant points out the importance of understanding the number of centimeters in a meter as a foundational aspect of unit conversion, emphasizing the need for careful attention to multiplying factors.
  • One participant discusses the relationship between \(\epsilon_0\) and \(\mu_0\) in SI units, noting that \(1/(4\pi\epsilon_0)\) equals \(c^2\) and mentioning the historical context of introducing c as a ratio between electric charges in different phenomena.
  • A final participant provides a straightforward example of unit conversion, illustrating that 100 cm/s equals 1 m/s, reinforcing the concept of unit equivalence.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the treatment of c in the conversion process, with some expressing confusion and others providing differing perspectives on the mathematical relationships involved.

Contextual Notes

The discussion highlights potential limitations in understanding unit conversions, including the need for clarity on definitions and the mathematical steps involved in relating different unit systems.

RAFIQ MULLA
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In conversion of formula from cgs into SI, usually c, the velocity of light is divided. Why it is so?
 
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Hi RAFIQ. Welcome to the forum.

You need to explain a little more. What is divided by what? Can you give an example?

In converting from cgs into SI, usually there is no division of c or by c. So it is very confusing what you mean.
 
How many cms are there in a m? Your answer could involve that, perhaps.
Conversions between units can be tricky unless you are scrupulous with all your multiplying factors.
 
[itex]1/(4\pi\epsilon_0)[/itex] in SI units is equal to c^2, with factors of ten coming in in the conversion from cgs to MKS.T his comes from [itex]\epsilon_0\times \mu_0=1/c^2[/itex]. [itex]\mu_0[/itex] is not a fundamental constant, but just comes from
[itex]\mu_0/4\pi=10^{-7}[/itex] with the factor [itex]10^{-7}[/itex] coming from the different units. There is also a factor of ten due to the difference between the original absolute Ampere and the SI Ampere.
Historically, the c came as the ratio between the electric charge that was natural for the current in magnetic phenomena and the electric charge that occurred in electrostatic phenomena. In order to use only one charge, the factor c was introduced.
 
Last edited:
100 cm/s = 1 m/s because 100 centimeters are one meter.
The same applies to multiples of this speed.
 

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