TBR Electrostatics

[dartmed]

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Which of the following does NOT decrease the work required to move one droplet against the electrostatic force, from the positively charged plate to the negatively charged plate?

I. Increasing the battery voltage
II. Decreasing the droplet charge
III. Increasing the droplet mass

I got the question right through POE, but I don't understand as to why option III is correct? Can anyone explain this to me? Thanks!

 

[anon4895]

Which of the following does NOT decrease the work required to move one droplet against the electrostatic force, from the positively charged plate to the negatively charged plate?

I. Increasing the battery voltage
II. Decreasing the droplet charge
III. Increasing the droplet mass

I got the question right through POE, but I don't understand as to why option III is correct? Can anyone explain this to me? Thanks!

Force times displacement (or distance, they're pretty interchangeable here). None of these options change the distance. Increasing the battery voltage will increase the charge on the plates, affecting the force. Decreasing the droplet charge will also affect the force. Changing the mass of the droplet does not affect the electric force whatsoever.

That's my best reasoning at least.

 

[dartmed]

Force times displacement (or distance, they're pretty interchangeable here). None of these options change the distance. Increasing the battery voltage will increase the charge on the plates, affecting the force. Decreasing the droplet charge will also affect the force. Changing the mass of the droplet does not affect the electric force whatsoever.

That's my best reasoning at least.

I got that far 😛, but the answer choice claims that choice III is also true...me don't get it.

 

[anon4895]

I got that far 😛, but the answer choice claims that choice III is also true...me don't get it.

Wait I'm a little confused here. Do you mean choice 3 is only one correct answer? I think both 1 and 3 are correct. 1 will affect the work but it will not decrease it... which is what the question says.

 

[dartmed]

Wait I'm a little confused here. Do you mean choice 3 is only one correct answer? I think both 1 and 3 are correct. 1 will affect the work but it will not decrease it... which is what the question says.

Ok, so I initially thought choice III is true since it won't affect it at all. However, TBR says something about charge density? How if you increase the mass, then you also increase the charge? Should I just ignore the explanation?

 

[anon4895]

Ok, so I initially thought choice III is true since it won't affect it at all. However, TBR says something about charge density? How if you increase the mass, then you also increase the charge? Should I just ignore the explanation?

Was there a passage before the question? I think the droplet is made up of a liquid that contains charge. That means that increasing the size of the drop will add to the charge.

To use a little bit of math (sorry)

charge density = charge/volume ---> (charge density)x(volume) = charge

since volume = mass x density we can say:

charge = (charge density)x(mass)x(density)

So increasing mass would increase charge.


I really don't like that question if it wasn't prefaced with anything, but I think this is what they meant.

 

[V5RED]

Ok, so I initially thought choice III is true since it won't affect it at all. However, TBR says something about charge density? How if you increase the mass, then you also increase the charge? Should I just ignore the explanation?

Without getting the specific explanation and the specific passage, it will be very tough to tell you if their explanation is good or bad. All we have right now is a straw man version of their explanation.

 

[Mornhavon]

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