Why am I getting two different results in emu and SI unit?

In summary, the conversation discusses the calculation of force between two magnetic poles, one unit pole apart, in electromagnetic and SI units. While the formula for force in electromagnetic units yields a result of 1 dyne, the formula in SI units does not match due to an error in the value of ##k_A##. It is recommended to work with units to spot errors.
  • #1
faheemahmed6000
18
0
I am computing force between two magnetic poles each of one unit pole (in emu) and situated one centimeter apart.

In electromagnetic units:
##F_{dyne}=\dfrac{p^2}{r_{cm}^2}=\dfrac{1^2}{1^2}=1 dyne##
where ##p## is pole strength in emu

In SI units:
##F_{N}=k_A \dfrac{P^2}{r_m^2}=10^{-7} \dfrac{({1.25\times 10^{-7}})^2}{10^{-4}}=1.5625 \times 10^{-17} \neq 10^{-5}N=1dyne##
where ##P## is that same pole strength in SI units

with ##P=1.25\times10^{-7}p## (see here)

Now why am I getting two different results in emu and SI for the same configuration?
 
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  • #2
The units in the formula "in SI units" don't match, at least not if ka is supposed to be ##\frac{\mu_0}{4 \pi}## as the numerical value used for it would suggest.
Working with units helps to spot errors.
 
  • #3
mfb said:
The units in the formula "in SI units" don't match, at least not if ka is supposed to be ##\frac{\mu_0}{4 \pi}## as the numerical value used for it would suggest.
Working with units helps to spot errors.
Please can you explain a bit more elaborately?
 
  • #4
Work with units, then the problem will become clear.
 
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  • #5
faheemahmed6000 said:
In electromagnetic units:
##F_{dyne}=\dfrac{p^2}{r_{cm}^2}=\dfrac{1^2}{1^2}=1 dyne##
where ##p## is pole strength in emu
I agree with @mfb. You need to show the units in each of your intermediate steps. As it is, I can tell that F is in dyne and r is in cm, but I cannot tell if p is in abC or statC. If it is abC then your equation is wrong, and if it is in statC then you are using electrostatic units not electromagnetic units.
 

1. Why do we have two different units of measurement for the same quantity?

The emu (electromagnetic unit) and SI (International System of Units) are two different systems developed to measure physical quantities. The emu system is based on the fundamental properties of electricity and magnetism, while the SI system is based on seven base units and their derived units. These two systems were developed at different times in history and have been used in different fields of science.

2. How do emu and SI units differ from each other?

The main difference between emu and SI units is in the way they are defined and the fundamental quantities they are based on. The emu system is based on the fundamental properties of electricity and magnetism, while the SI system is based on seven base units: meter, kilogram, second, ampere, kelvin, mole, and candela. Additionally, the units in the emu system are not always consistent with the units in the SI system, leading to different numerical values for the same physical quantity.

3. Which unit of measurement should be used for scientific research?

The SI system is the most widely used and accepted system for scientific research. It provides a standardized and consistent way to measure physical quantities and allows for easier communication and comparison between researchers. However, in certain fields such as electromagnetism and electrical engineering, the emu system may still be used.

4. Can emu and SI units be converted to each other?

Yes, it is possible to convert between emu and SI units using conversion factors. However, it is important to note that the conversion will not always result in a simple numerical value, as the two systems are based on different fundamental quantities.

5. Are there any advantages to using emu units over SI units?

In certain fields, such as electromagnetism, the emu system may be more convenient and provide more accurate results. This is because the emu system is based on the fundamental properties of electricity and magnetism, making it more applicable to these fields. However, in most scientific research, the SI system is preferred for its consistency and widespread use.

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