- #1
Angello90
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If E=-∇V, does it mean that negative voltage emits positive electric field, and positive v negative ef?
Electric field with reference to voltage
- Context: Undergrad
- Thread starter Angello90
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Discussion Overview
The discussion revolves around the relationship between electric fields and voltage, particularly focusing on the implications of the equation E = -∇V. Participants explore definitions, interpretations of electric field direction, and specific examples involving potential differences and their effects on electric fields.
Discussion Character
- Conceptual clarification
- Debate/contested
- Mathematical reasoning
Main Points Raised
- One participant questions whether negative voltage results in a positive electric field and vice versa.
- Another participant suggests that the direction of the electric field is defined by the movement of positive charges, indicating that the field points towards the negative plate in a capacitor setup.
- A participant presents a specific problem involving a potential difference equation and expresses confusion regarding the electric field on either side of a charged slab.
- There is a clarification that the gradient in the equation E = -∇V represents the change in potential over distance, not a direct emission of the field.
- Participants discuss the mathematical derivative of the potential difference equation, confirming the calculation of the electric field.
- One participant explains the negative sign in the context of the electric field pointing towards the negative side, emphasizing the relationship between potential and field direction.
Areas of Agreement / Disagreement
Participants express differing interpretations of the relationship between voltage and electric fields, with some agreeing on the definitions while others challenge or seek clarification on specific points. The discussion remains unresolved regarding the implications of negative voltage and its effect on electric fields.
Contextual Notes
There are unresolved assumptions regarding the definitions of voltage and electric fields, as well as the specific conditions under which the discussed equations apply. The discussion also highlights potential confusion over terminology and mathematical expressions.
- #2
sophiecentaur
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It's basically a matter of definition.
I think you can look at it this way: The field between a positive plate and a negative plate is said to be directed towards the negative plate (the direction in which a positive charge would move) but the positive plate has a positive potential with respect to the negative plate i.e. voltage increases in the opposite direction to the direction of the force on a positive charge.
I think you can look at it this way: The field between a positive plate and a negative plate is said to be directed towards the negative plate (the direction in which a positive charge would move) but the positive plate has a positive potential with respect to the negative plate i.e. voltage increases in the opposite direction to the direction of the force on a positive charge.
- #3
Angello90
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you see I have this question where youre give an equation for potential deference of 10-5z^2, so E= -10z right?, anyway there is a field on one side of the slab (slab is the material with a charge) and it asks about EF on both sides, ie what is EF on right hand side and left hand side. As a hint there is "watch the sign" statement. So I am really confused 
- #4
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Angello90 said:
That is not what the Grad means! It is the CHANGE in potential over a distance, i.e. a gradient. In 1 dimension, it is E = -dV/dx.
Zz.
- #5
Angello90
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Yeah and d(10-5z^2)/dz=-10z, am I correct?
- #6
sophiecentaur
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Uh?
If you want a simple explanation for the sign, the field points towards the negative side and away from the positive. i.e. a negative slope as distance towards the positive increases - hence the negative sign.
Note. A field isn't "emitted".
If you want a simple explanation for the sign, the field points towards the negative side and away from the positive. i.e. a negative slope as distance towards the positive increases - hence the negative sign.
Note. A field isn't "emitted".
- #7
Angello90
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Ok thanks a lot sophiecentaur, and yeah i know field isn't emitted, that's why i used "emitted" not emmited;) thanks guys
- #8
sophiecentaur
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Angello90 said:
It was terminology I was referring to - not spelling
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