Why Is the Conversion Between CGS and SI Units in Electromagnetism Confusing?

• Alireza_M
The conversion factor is used to convert between the cgs unit of Oersted and the SI unit of Ampere per meter. In summary, the conversion coefficient between cgs and SI units for vacuum permeability is 1000/(4 x pi).
Alireza_M
Dear friends,

As you know, in CGS units we have vacuum permeability as unity (1). so H=B and we use Oersted for H.
on the other hand, in SI, permeability is (4 x pi x 0.0000001) and we use Ampere per meter for H. unfortunately after trying for couple hours, I couldn't derive the algebra of converting these to each other. everywhere they simply say just multiply 1000/(4 x pi) to amper per meter. but why? and how to derive this conversion coefficient?

I know that cgs is cm gram second and si is meter kilogram second and i know how to convert these, but when amperes come into play and when the formulas are different in a coefficient, I just get confused.

I apologies in advance if this looks ridiculous.

Thread moved to General Physics, where more people might see it.

Alireza_M said:
everywhere they simply say just multiply 1000/(4 x pi) to amper per meter. but why? and how to derive this conversion coefficient?
You cannot derive it. It is just a definition. There is no deeper reason besides the fact that is how the SI units are defined.

1. What is the difference between CGS and SI units in electromagnetism?

CGS (Centimeter-Gram-Second) and SI (International System of Units) are two systems of measurement commonly used in electromagnetism. The main difference between them is the unit of measurement for electric charge. In CGS, the unit of electric charge is the statcoulomb (statC), while in SI, it is the coulomb (C). Additionally, CGS uses centimeters, grams, and seconds as base units, while SI uses meters, kilograms, and seconds.

2. Which system of units is more widely used in electromagnetism?

SI units are more widely used in electromagnetism, particularly in modern research and technology. This is because SI units are more consistent and easier to use in mathematical equations. However, CGS units are still used in some specialized fields.

3. How do you convert between CGS and SI units in electromagnetism?

To convert between CGS and SI units in electromagnetism, you can use conversion factors. For example, to convert from statC to C, you can use the conversion factor 1 statC = 3.3356 x 10^-10 C. Similarly, to convert from gauss (CGS unit for magnetic flux density) to tesla (SI unit for magnetic flux density), you can use the conversion factor 1 gauss = 10^-4 tesla.

4. Why are SI units considered to be more scientifically accurate in electromagnetism?

SI units are considered to be more scientifically accurate in electromagnetism because they are based on fundamental physical constants, such as the speed of light and the charge of an electron. This makes them more precise and consistent, allowing for more accurate measurements and calculations.

5. Can CGS and SI units be used interchangeably in electromagnetism?

While it is possible to use CGS and SI units interchangeably in electromagnetism, it is generally not recommended. Mixing units can lead to errors and confusion, and it is best to stick to one system of measurement for consistency.

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