Berkeley Review Physics problem

[Maxine450]

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I really hate this chapter. If someone could help me out with these problems that would be great. It's on book 2, page 154 passage III. I got nearly all of these wrong.

11. On occasion, the electrons are made to pass through the plates undeflected. If the electrons enter the region between the plates with the same direction but with excessive velocity:
On the previous page it talks about velocity selectors and how if the velocity is excessive, the particle will be deflected upward. Which is why I'm confused why the answer is B) they will be deflected downward.

18. Assume a cation enters an electric field oriented as shown below. Which path BEST represents the path of the ion?
In the picture the electric field points down and theres an arrow deflecting up, straight across, and down
The answer: it deflects down.

I'm really confused as to how to solve this problem. Right hand rule? Does it make a difference if the particle is an electron or a proton?

19. Which will not be deflected by a magnetic field?
a. a moving electron
b. an orbiting proton
c. a fixed anion
d. an accelerating cation
The answer is C. i really don't get this.

Help mee!

 

[kehlsh]

wrong forum dood

 

[Maxine450]

The BR teach never posts on that forum so I'm trying it here instead.

 

[liveoak]

it has to be moving to experience a force iirc.

 

[circulus vitios]

19. Somewhere in the chapter it is mentioned that magnetic fields can only have an affect on moving charged particles. This is because magnetic fields interact with one another. All moving charges generate a magnetic field, thus giving the other field something to interact with. A magnetic field cannot directly interact with just the charge. It needs a magnetic field to be present. A fixed (ie, non-moving) anion will be not affected because it is not moving and therefore generates no magnetic field.

 

[circulus vitios]

11. It's asking about an electron. Electrons are negatively charged. In the example of velocity selectors they use a positively charged particle. The right hand rule (and direction given in the velocity selector example) are valid for positively charged particles. When you use a negatively charged particle you change the direction of the vector given by the right hand rule.

 

[circulus vitios]

18. I can't remember this diagram off the top of my head. It's just an electric field, right? No magnetic fields? The field lines of an electric field always show the direction a positively charged particle would take. Cations are positively charged so it should travel in the direction of the field lines.