How did JJ Thomson find the charge-to-mass ratio for an electron?

posted Feb 7, 2018, 6:16 AM by Barbara Fortunato   [ updated Feb 16, 2018, 12:41 PM by Barbara Fortunato ]
2: Th 2/15, 4: Th 2/15
 
Today, after our daily quiz, we'll use a cathode ray tube to repeat the experiments of J.J. Thomson.  In doing so we'll review how a charged particle behaves in an electric and a magnetic field.  For the next class, write in your journals the derivation of the magnetic field from a coil and your calculated value for q/m.  List at least 5 sources of possible error.  Your calculated value should be within an order of magnitude of the accepted value. 
 
To get a visualization of the magnetic field between Helmholtz coils, check out this video, where you can see that in the center region, the magnetic field is fairly uniform.

Helmholtz Coil - B field visualization

 
Homework:  No Homework Weekend!  (but make sure you've watched the Lenz's Law videos from last week.
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