How to Convert Cgs to SI Units for Flux and Energy Values?

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Discussion Overview

The discussion revolves around converting values from CGS (centimeter-gram-second) units to SI (International System of Units) for flux and energy values, specifically focusing on the conversion of millijanskys (mJy) and a flux value expressed in cm²·g⁻¹.

Discussion Character

  • Technical explanation, Debate/contested, Homework-related

Main Points Raised

  • One participant presents a value of 10.7 mJy and proposes a conversion to SI units, suggesting it might be 1.7*10^(-2)*10^(-26), but expresses uncertainty about this calculation.
  • The same participant also discusses converting a flux value of kappa from cm²·g⁻¹ to m²/kg, initially suggesting it might be 2*10^(-7) m²/kg, while indicating uncertainty in the conversion process.
  • Another participant challenges the grams conversion, stating that the negative exponent is incorrect and suggests that division by 10^(-3) should be used instead of multiplication.
  • A different participant provides a breakdown of the conversion for 10.7 mJy, clarifying that it equals 1.07 × 10^(-2) and emphasizes the importance of maintaining precision in the conversion process.
  • This participant also includes a reference to the definition of the Jansky (Jy) and its relation to SI units, specifically noting that 1 Jy = 10^(-26) W/(m²·Hz).

Areas of Agreement / Disagreement

Participants express differing views on the correct approach to the conversions, particularly regarding the treatment of negative exponents in the conversion from grams to kilograms. The discussion remains unresolved as participants have not reached a consensus on the correct conversion factors.

Contextual Notes

There are limitations in the discussion regarding the assumptions made in the conversion processes, particularly the treatment of units and the handling of negative exponents. Some mathematical steps are not fully resolved, leaving ambiguity in the proposed conversions.

SorenaJ
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Hi

I have a value that is 10.7 mJy, that I need to convert to SI units. I thought it would be 1.7*10^(-2)*10^(-26) but that might be wrong?

Then I have a flux value, kappa, of 2 cm^2.g^(-1) that needs to be converted to meters and kilogram. I thought it was 2*10^(-7) m2/kg, but that might be wrong as well. I would get the 10^(-4) from converting from cm2 to m2 and the 10^(-3) from converting from g to kg.

Can anyone help?
 
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In the second part, you have the grams conversion wrong because it has a negative exponent. You should be dividing by 10^(-3), not multiplying by it.

I have no idea what a mJy is, but the 10^(-26) is a truly large factor.
 
SorenaJ said:
Hi

I have a value that is 10.7 mJy, that I need to convert to SI units. I thought it would be 1.7*10^(-2)*10^(-26) but that might be wrong?

10.7 = 1.07 × 10

10.7 m = 10.7 × 10-3 = 1.07 × 10-2

Don't drop those zeroes!

BTW, this is the definition of the Jansky (Jy):

https://en.wikipedia.org/wiki/Jansky

1 Jy = 10-26 W / (m2-Hz)
 
Thank you!
 

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