Electric field lines of H2O molecule

AI Thread Summary
The discussion focuses on the electric field lines of the H2O molecule, specifically addressing issues in the calculations for parts (a), (b), (c), and (d) of a problem. Part (a) is incorrect as the integration of volume charge density should yield zero, and the charge should be modeled as uniformly distributed over a conducting sphere. In part (c), the number of electric field lines must reflect the enclosed charge, requiring a proper understanding of charge distribution, particularly with respect to the two electrons. Participants emphasize the need for Dirac delta functions to accurately represent charge densities and clarify that protons should be treated as point charges. Overall, the conversation highlights the importance of correctly applying electrostatic principles to analyze the H2O molecule's electric field.
guyvsdcsniper
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Homework Statement
In the limit R=0, e.g., when the Oxygen ion is a point charge:
a) Write down the volume charge density (15pts)
b) Draw the electric field lines far away from charges (25pts)
c) Draw the electric field lines near the point charges (25 points)
d) At finite radius R, draw the lines near the charges
Relevant Equations
p=q/v
I wanted to post my work so far to see if I am on the right path toward the correct answer so far.

I have attached a ss of the actual problem and my work in the attachments
IMG_0336.jpg


Screen Shot 2022-02-16 at 7.04.19 PM.png
 

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Part (a) does not look correct. Remember, when you integrate the volume charge density over all space, you should get zero. Also, you are told to model the oxygen as a conducting sphere of radius R. Is the charge distributed uniformly over the volume of the sphere?

Part (c) needs some fixing. You must have twice as many lines going into the sphere as coming out of either one of the charges. Do you see why? Parts (b) and (d) look OK.
 
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kuruman said:
Part (a) does not look correct. Remember, when you integrate the volume charge density over all space, you should get zero. Also, you are told to model the oxygen as a conducting sphere of radius R. Is the charge distributed uniformly over the volume of the sphere?

Part (c) needs some fixing. You must have twice as many lines going into the sphere as coming out of either one of the charges. Do you see why? Parts (b) and (d) look OK.
for part (a) it should be zero because I followed the diract delta function, I should get a spike at the center and zero all over space correct?

part (c), Is this due to having 2 electrons?
 
quittingthecult said:
for part (a) it should be zero because I followed the diract delta function, I should get a spike at the center and zero all over space correct?

part (c), Is this due to having 2 electrons?
You need Dirac deltas for all three charges. When you put charge -2e on a conductor of radius R, does the charge go to the center?

For part (c) draw Gaussian surfaces around each charge. The number of electric field lines coming out or going in must be proportional to the enclosed charge.
 
kuruman said:
You need Dirac deltas for all three charges. When you put charge -2e on a conductor of radius R, does the charge go to the center?

For part (c) draw Gaussian surfaces around each charge. The number of electric field lines coming out or going in must be proportional to the enclosed charge.
No it wouldn't go to the center. It would spread evenly on the surface. So for the electron it should be,
gif.gif
?
I am not sure about the protons though? I don't know the center of the protons.
 
quittingthecult said:
No it wouldn't go to the center. It would spread evenly on the surface. So for the electron it should be,
View attachment 297216?
I am not sure about the protons though? I don't know the center of the protons.
You mean for the ion, not electron. Start by stating what the charge density functions should be over three ranges centred on the ion: 0 to R, R to d, and > d. Then try to figure out how to write that in ##\delta## functions. And don't confuse the ##\delta## function with its integral.

You are told to treat the protons as point charges.

In c) you are only asked for the field lines near the protons. Though it is not made very clear, d) is the corresponding question for the ion, and the figure should not show the protons.
 
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