How can the force NOT be zero here?

[flyingpig]

Homework Statement

http://www.electron.rmutphysics.com...erway-Beichne 6edr-4/29 - Magnetic Fields.pdf

Go to page 17 to 18 (it cuts off there), in the picture the vectorial sum of the forces are CLEARLY 0 (they even took the effort of bolding and adding an arrow to it), so how come they are still adding the "total force"?

 

[Berko]

What page in the book? I don't se any pages labeled 17 and 18.

 

[flyingpig]

In the pdf

 

[Berko]

I loaded the pdf. It starts on page 894.

 

[flyingpig]

There are 32 pages

 

[fluidistic]

Are you talking about the "Active figure 29.23"?
If so you're right that the total force is zero, but I see nowhere why it couldn't be zero.

They talk about the Lorentz force which isn't necessarily zero and is precisely zero in the special case of the figure 29.23. It can of course be zero in other (hypothetical at least) situations.

Where did you read that the force is NOT zero? What page exactly?

 

[flyingpig]

I didn't read anywhere that it isn't zero, the picture tells me. The force is equal in magnitude and opposite direction

 

[Apphysicist]

Just a bit further down the same page, the point is that the velocity selector allows a charged particle with a certain velocity to shoot straight down the finely tuned system between the plates and in the magnetic field unimpeded. Presumably, if it veers off the middle line just a bit, the particle will be "discarded" if you will. Then, a slit at the end of the velocity selector will allow those particles that are of the certain velocity (v=E/B...and you can tune your velocity selectors E and B fields to get that specific velocity) to continue onward (such as in a mass spectrometer where you want to be sure of the initial velocity...stick a velocity selector in front of your mass spectrometer region, like in the next figure).

The net force is only 0 for those particles with v=E/B.