Electric Field Direction Convention

[justadream]

If an electric field is "directed towards" the right, can I immediately conclude which side the + and - sides are?

Or, does that depend on what exactly I am using the electric field for (e.g., to push electrons or to push protons)?

For example, if I wish to push protons to the right, I know that means I need "+ -" but is that an electric field directed to the right or left?

Likewise, if I wish to push electrons to the right, I know that means I need "- +" but is that an electric field directed to the right or left?

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[ayocaptain628]

The convention is for electric field vectors to point in the direction that a positive charger would go
So if the lines are pointing left to right a proton would move left to right
Conversely an electron would move right to left with the same electric field.
So you would want an electric field to go left if you wanted to push an electron to the right

The same electric field will push an electron and a proton in opposite directions, you don't need a separate field to push one and then the other.

The intrinsic nature of the electric field is that the direction of opposite charges will also be opposite. Ie proton up? Electron must go down.

In fact all fields in the E and M unit are like that. That's why we don't need to change the direction of the electric or magnetic field when using a velocity selector. If we use a proton or if we use an electron, the fields will act accordingly depending on the charge. Despite the direction of the forces being in opposite directions if its a positive negative charge.

 

[costales]

If you want an electron to go to the right, pretend it's a proton going to the left, so your E vector has to point to the left (because that's where the electric force F = qE is pointing for the proton). And yes, you can always say that the tip of the E vector is on the more "-" side and the tail is on the more "+" side, since the E vector always points "downhill" i.e. to a lower potential.

 

[NextStepTutor_1]

Electric field lines (the arrows that represent direction of the electric field) point in the direction that a positive charge travels.
So if the electric field was pointing in the right direction, as such:
---------->
+ ............... -
Then the proton/cation moves in the same direction, from left to right, and the schematic placement of charge is positive on the left and negative on the right (makes sense because opposites attract and we know the proton/cation must move to the right).
If the charge was negative and placed in the same electric field, it would move from right to left or against the direction of the electric field lines.

Cheers!



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