Charge to mass ratio (1 Viewer)

[CHUDYMASTER]

I don't understand JJ's experiment. What was the significance of equalling the magnitude of the magnetic/electric fields to make a single beam of cathode rays?? Why not just measure the defection of each, individually?

Furthermore, what is the significance of the charge-to-mass ratio? Does it just show that cathode rays (electrons) are fundamental particles?

 

[+:: $i[Q]u3 ::+]

He didnt' know the mass of an electron, or the charge.
So Thomson couldn't have measured the effect of the fields individually (he had too many unknowns in his equations).
It was only by allowing the E-field and the B-field to directly oppose each other that he could establish the ratio. (they were oriented at right angles such that the roces they produced on the cathode rays directly opposed each other; like.. the e-field's pushing the ray up, the b-field's pushing it down, but since they're equal they cancel out)
It was up to Millikan to rigure out the actual mass and the charge.

 

[inasero]

i think in macmillan physics they talk about the significance of the effect of the electric field equalling the effect of the magnetic field on a charged particle...
he established an equivalence to derive another formula:

Force of B field = Force of E Field
therefore qvB = qE
therefore E = vB <-----important as it establishes a
quantitative relatioship between
the electric field, velocity of particle and
the magnetic field