Mass Spectrometer.....

[sps27]

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Would appreciate some insight with this question in TBR i.e., page 159, Question 41 of TBR Physics part 2.

The passage is on Mass Spectrometer and the diagram shows 2 regions 1 (velocity selector) and region 2 (deflection). The question specifically mentions cations accelerated in region 1 from left to right and then they get deflected in region 2. The battery connections show + (Cathode) connected to one of the parallel plates and - (anode) connected to another end. The anode end is closer to region 2 and has a small hole through which these particle enter region 2. The Cathode is on the left side and Anode is on the right side. And the direction of cations moving is from Cathode to Anode.

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Question: To accelerate anion particles from left to right in Region 1, and deflect those particles out of the page in Region 2, how must the E and B fields be aligned in Figure 1.

a) Anode plate left, cathode plate right, B field up
b) Anode plate left, cathode plate right, B field down
c) Anode plate right, cathode plate left, B field up
d) Anode plate right, cathode plate left, B field down

The Ans given is d). The explanation is - Anion particle migrate from the Cathode to anode in uniform electric field, so in order to accelerate the anionic particles from left to right, the anode must be on the right side and cathode must be on the left side as in Region 1.
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My confusion is, Anion particle are negatively charged. Right? How do they migrate cathode(+) to anode(-) in uniform electric field ??? Beats me....I guess....

 

[sps27]

somebody please ?

 

[Romz]

Would appreciate some insight with this question in TBR i.e., page 159, Question 41 of TBR Physics part 2.

The passage is on Mass Spectrometer and the diagram shows 2 regions 1 (velocity selector) and region 2 (deflection). The question specifically mentions cations accelerated in region 1 from left to right and then they get deflected in region 2. The battery connections show + (Cathode) connected to one of the parallel plates and - (anode) connected to another end. The anode end is closer to region 2 and has a small hole through which these particle enter region 2. The Cathode is on the left side and Anode is on the right side. And the direction of cations moving is from Cathode to Anode.

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Question: To accelerate anion particles from left to right in Region 1, and deflect those particles out of the page in Region 2, how must the E and B fields be aligned in Figure 1.

a) Anode plate left, cathode plate right, B field up
b) Anode plate left, cathode plate right, B field down
c) Anode plate right, cathode plate left, B field up
d) Anode plate right, cathode plate left, B field down

The Ans given is d). The explanation is - Anion particle migrate from the Cathode to anode in uniform electric field, so in order to accelerate the anionic particles from left to right, the anode must be on the right side and cathode must be on the left side as in Region 1.
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My confusion is, Anion particle are negatively charged. Right? How the hell do they migrate cathode(+) to anode(-) in uniform electric field ??? Beats me....I guess....

Hmm, I don't have the picture but I would assume its because the Anode is the source of higher Voltage in comparison to the cathode.

I know that electros travel from low Electric Potential to higher electric potential, in that respect. Either mistake in the book, or battery (which I don't have an image of...) is connected such that Anode is area of higher E potential.

 

[Romz]

Yeah it's a battery thing.

The cation thing is throwing me off tho.

 

[nOchemallday]

The reason a cathode is called such is because it attracts cations, not because it acts like a cation. In other words the Cathode is the negatively charged electrode and therefore attracts cations an repels anions.

Conversely the anode attracts anions. therefore to accelerate the anion to the right, the anode must be placed on the right.

 

[Romz]

And the direction of cations moving is from Cathode to Anode.

Conversely the anode attracts anions. therefore to accelerate the anion to the right, the anode must be placed on the right.

Som1 is wwrrroongg

 

[FeinMS]

Anode is assigned as + and anions are attracted to it. Cathode is assigned as - and cations are attracted to it. Electrons, however, moves from anode to cathode. Different definition of galvanic cell.

 

[sps27]

Som1 is wwrrroongg

Well, this whole question is a little iffy..... I still don't get it. I have to spend some more time on it. Still thinking about it........

As goes for the definition of anode and cathode, I know it can get very very confusing but the bottom line is - it all depends on what cell you are talking about. In a galvanic aka voltaic cell cathode is +ve, anode is -ve. In an electrolytic cell, anode is +ve and cathode is -ve and the reason for that is because of migration of anions towards anode and cations towards cathode. But that is only for an electrolytic cell, not galvanic cell. The cell, batteries we use in circuits etc., are all galvanic cell. So for those, the current runs from cathode to anode, cathode being +ve and anode being -ve.

Kaplan does an excellent job in explaining this concept in Gen Chem book - chapter on electrochemistry. If you have the time go through it, it will make things crystal clear for you.

 

[sps27]

Hello Berkley Review Tech. Could you please explain this problem from TBR. Thank you!