TBR chapter 8 passage 3 #11 Velocity selector

[crazy person]

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I'm a little bit confused with this question:

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 an excessive velocity:

a) they will be deflected upwards
b) they will be deflected downward
c) they will remain undeflected
d) they will be turned back the way they came

This problem is a cathode ray tube where it shows an anode on top and a cathode on the bottom.

The answer is b.

I'm not understanding why the answer is not A? I thought that if V is too fast then it deflects upwards
FB > FE according to TBR notes.

Is it necessary to use the right hand rule for this problem?

Thanks guys !!!

 

[BerkReviewTeach]

The right hand rule is for a positive particle, so when dealing with an electron, the opposite behavior is observed. This is basically a bit of a trick question, but one that is completely within the realm of realistic probability.