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J j thomson's previous experiment 
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#1
Mar1004, 11:09 PM

P: 1,046

I thought I was going to like this book, but it's defying me.
I'm staring at pg 123 of Tipler's Modern Physics text (3rd ed.) This is talking about an experiment he says Thomson did before the "famous" J J Thomson experiment. It goes like this: Anyway, on the preceding page, he talks a bit about the circular path followed by charged particles in a magnetic field and gives [tex] quB = \frac{mu^2}{R}[/tex] Obvious enough. (Here, little q is of course the charge on an individual particle, so it corresponds to e, not Q, in the other equations.) But I don't see how that helps in getting to equation 33 above. All I get from the two preliminary equations is [tex]\frac{e}{m} = \frac{Qu^2}{2W} [/tex] To get from that to his equation 33 I have to say [tex]u^2 = \frac{4W^2}{B^2R^2Q^2}[/tex] and I don't see anything that lets me say that. Any ideas? 


#2
Mar1004, 11:30 PM

P: 988

I'm not familiar with Thomson's "previous" experiment, but if you look at the two equations:
[tex] quB = \frac{mu^2}{R}[/tex] and [tex]\frac{e}{m} = \frac{Qu^2}{2W} [/tex] If you solve for u in the first equation you get [tex]u = \frac{eBR}{m}[/tex] which you can then substitute into the second equation to get the desired equation. cookiemonster 


#3
Mar1004, 11:42 PM

P: 1,046

Hmmm...I hate to admit to how long I didn't see that. Thanks for providing the requisite smack in the head. 


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