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"This was proven in 1903 by J. J. Thomson who calculated that the momentum of the electrons hitting the paddle wheel would only be sufficient to turn the wheel one revolution per minute."

This is a line from Wikipedia page.

J.J Thomson measured the charge to mass ratio of electron in year 1897, and R.K Millikan measured charge of electron in year nearly about 1910 i.e. Thomson knew only the charge to mass ratio of electron in 1903.

Then how did he was able to determine the momentum of electron when he didn't knew the mass of electron ?

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  • $\begingroup$ physics.princeton.edu/~mcdonald/examples/thomson.pdf $\endgroup$ – Zhe Aug 7 at 14:16
  • $\begingroup$ Another way to put it is that the computed radiation pressure is too small: en.wikipedia.org/wiki/Radiation_pressure $\endgroup$ – Zhe Aug 7 at 14:17
  • $\begingroup$ Recall that momentum is the product of mass and velocity. You don't need to know the mass or velocity of the objects hitting something and transferring momentum to something else - you just need to know the mass and velocity of what is being hit. $\endgroup$ – Jon Custer Aug 7 at 15:06
  • $\begingroup$ Might be a good question to ask at physics SE. $\endgroup$ – Buck Thorn Aug 7 at 19:30

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