Mass of Electron: 9.10938291x10-31 kg

In summary, the value for the mass of an electron, according to Wikipedia, is 9.10938291(40)×10−31 kg, which means that there is an experimental uncertainty of 0.00000040×10−31 kg in the last two digits. This value is dependent on other constants such as the Rydberg constant, Planck's constant, and the fine structure constant. Any changes in these values will also affect the value for the mass of an electron.
  • #1
johann1301
217
1
When i look up the mass of an electron, wikepedia says: 9.10938291(40)×10−31 kg

Fine, but what does the (40) stand for? Is there 40 more or total decimals, or is there uncertainty in weather the 40 belongs there or not?

or some other reason maybe??

:)
 
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  • #2
9.10938291(40)×10−31 kg means 9.10938291×10−31 kg +- 0.00000040×10−31 kg
Numbers in parentheses are experimental uncertainty in the last given digits.
 
  • #3
Thanks;)
 
  • #4
It means that 9.10938291 have all been confirmed the right values, and its a prediction that the next 2 numbers are 4 and 0
Thanks,
Z.c
 
  • #5
I realize this topic is a bit dated, but still worth a quick follow-up...
dazza95 said:
It means that 9.10938291 have all been confirmed the right values, and its a prediction that the next 2 numbers are 4 and 0
Thanks,
Z.c

Well... no, actually. As Khashishi noted, the 4 and 0 relate to standard uncertainty and are associated with the last two digits 9, 1, meaning that the value for electron mass is probably 9.10938291*10^-31 kg, plus or minus .00000040 * 10^-31. Easy to see if you go to the NIST site and check out the value for electron mass: http://physics.nist.gov/cgi-bin/cuu/Value?me

Furthermore, the mass of an electron is a dependent constant. It is not measured directly, but takes it's value from formulas such as the following: 2Rh/c*alpha^2 where R is the Rydberg constant, h is Planck's constant, c is the speed of light, and alpha is the fine structure constant. R has been measured to a high degree of precision, c is fixed by definition, h is increasingly being measured to a high degree of precision, leaving alpha, a constant the measurement of which you can read about on Wikipedia. See: http://en.wikipedia.org/wiki/Fine-structure_constant#Measurement. If any of the above values change, then so too does the value for electron mass.

Not sure how the standard uncertainty is calculated, but it's in some manner a combination of the standard uncertainty associated with R, h and alpha.

So, for example, numerically, using CODATA 2010 values, and without reference to units: (2Rh)/(c*alpha^2) = (2*1.0973731568539*10^7*6.62606957*10^(-34))/(299792458*137.035999074^(-2)) = 9.10938290*10^-31, which is off on the last digit, but that's almost certainly a rounding error.

- AC
 
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FAQ: Mass of Electron: 9.10938291x10-31 kg

What is the mass of an electron?

The mass of an electron is 9.10938291x10-31 kilograms.

How was the mass of an electron determined?

The mass of an electron was determined through a variety of experiments, including the Millikan oil drop experiment and the Thompson's cathode ray tube experiment. These experiments showed that the mass of an electron is approximately 9.10938291x10-31 kilograms.

Why is the mass of an electron important in science?

The mass of an electron is important in science because it is one of the fundamental properties of an electron and is used in many calculations and equations, particularly in the fields of quantum mechanics and atomic physics.

How does the mass of an electron compare to the mass of a proton?

The mass of an electron is much smaller than the mass of a proton, which is approximately 1.6726219x10-27 kilograms. The mass of an electron is about 1/1836 times the mass of a proton.

Can the mass of an electron change?

The mass of an electron is considered a constant and does not change under normal conditions. However, in certain extreme environments such as high energy particle accelerators, the mass of an electron can be affected by relativistic effects.

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