Direction of a positive charge's velocity in an electric field.

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Homework Help Overview

The discussion revolves around the behavior of a positive charge in an electric field, particularly focusing on the direction of its velocity and the relationship between electric potential and electric field. Participants are exploring concepts related to electric fields, potential gradients, and capacitors.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants express initial thoughts on the direction of a charge's velocity and question the conditions under which certain answers apply, such as the uniformity of the electric field. There are inquiries about the relationship between electric potential and electric field, as well as the implications of resistance on charge storage in capacitors.

Discussion Status

Some participants are providing hints and definitions related to electric fields and potential, while others are seeking clarification on concepts that were not covered in their coursework. Multiple interpretations of the questions are being explored, and there is an ongoing exchange of ideas without a clear consensus.

Contextual Notes

Participants mention that certain concepts, like potential gradients, were not taught in their physics class, indicating a gap in foundational knowledge that is affecting their understanding of the problems. There is also a reference to homework constraints and the need for hints rather than complete solutions.

theBEAST
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Homework Statement


Here is the question with the answer:
http://dl.dropbox.com/u/64325990/phys153Q/21.5.PNG

The Attempt at a Solution


I initially thought it would be A but it isn't and does anyone know why?
 
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hi theBEAST! :smile:
theBEAST said:
I initially thought it would be A but it isn't and does anyone know why?

wouldn't it only be A if the electric field was uniform? :wink:
 
tiny-tim said:
hi theBEAST! :smile:


wouldn't it only be A if the electric field was uniform? :wink:

Ohhhh thanks that makes sense.

I have another one:
http://dl.dropbox.com/u/64325990/phys153Q/23.9.PNG

I thought this was A, if you put a point charge there... How could it feel a force?
 
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what is the equation relating electric potential and electric field? :wink:
 
tiny-tim said:
what is the equation relating electric potential and electric field? :wink:

Hmmmm one is 1/r and one is 1/r^2 so would this mean E ≠ 0? Thus F is not zero? Not really sure.
 
you should know this definition :redface: …

the electric field is minus the gradient of the (scalar) potential …

E = -∇φ​

(what did you think the electric potential was for? :confused:)
 
tiny-tim said:
you should know this definition :redface: …

the electric field is minus the gradient of the (scalar) potential …

E = -∇φ​

(what did you think the electric potential was for? :confused:)

Thanks Tim, I kind of know the definition... The concept was potential gradients was not taught in our physics class but I did read some of it on my own online. They are related in that the derivative of potential with respect to x is the electric field. So I am not sure how I can relate it to the multiple choice question :S.

I hope I'm not asking too many question at once but it is getting late and I would love to get a hint at what I am doing wrong for this question as well (once I wake up :P):
http://dl.dropbox.com/u/64325990/phys153Q/26.9.PNG

I thought R would affect the maximum charge stored as well because it affects the V of the battery and so the equation C=Q/V?
 
Last edited by a moderator:
theBEAST said:
I thought R would affect the maximum charge stored as well because it affects the V of the battery and so the equation C=Q/V?

hint: when the capacitor C is fully charged, what is the voltage drop across the resistor R ? :wink:
 

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