How do we know if an electric field is negative or positive?

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SUMMARY

The discussion centers on understanding the nature of electric fields and their relationship with charged particles. An electric field is defined as a vector quantity with a magnitude expressed in N/C, indicating the force exerted on a unit positive charge. The direction of the force on a charged particle depends on the sign of the charge: a positive charge moves away from a positive electric field and towards a negative electric field. The confusion arises from mixing the concepts of electric charge and electric field, which are distinct entities in physics.

PREREQUISITES
  • Understanding of electric fields and their vector nature
  • Knowledge of Coulomb's law and the equation F = q * E
  • Familiarity with the concepts of positive and negative charges
  • Basic grasp of vector quantities in physics
NEXT STEPS
  • Study the properties of electric fields and their vector representation
  • Learn about the implications of charge polarity in electric fields
  • Explore the relationship between electric fields and forces on charged particles
  • Investigate the concept of electric potential and its relation to electric fields
USEFUL FOR

Students of physics, educators teaching electromagnetism, and anyone seeking to clarify the concepts of electric fields and charges.

x86
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Homework Statement


Note: this is actually my own question, not something from a book. So if I am wrong about some terminology please let me know

In physics questions, they will tell you an electric field is |Some Value|. Since |Some Value| (lets call it X) is always positive, how do we know if the field is negative or positive?

Homework Equations


F = q * E

The Attempt at a Solution


For example
An electric field has a force of x N/C and a charge of Y Coulombs is placed in the field.

If Y > 0, we know it is a positively charged particle
If Y < 0, we know it is a negatively charged particle

Now, if the question asks how to find the direction the particle moves in; how is this possible to determine?

Let's assume Y > 0 and it is a cation

If the electric field is positively charged, the direction of the cation will be AWAY from the electric field.

If the electric field is negatively charged, the direction of the cation will be TOWARDS the electric field.

Therefore, it is impossible to determine the direction (as far as I understand).

So, how can I determine the magnitude of the particle, if I don't know the charge of the field?

i.e. say E = 3 * 10^9 and q = 3 * 10^-9

Then F = 3 * 3 = 9 N

But in what direction will it be?

We also don't know where the field is positioned, so how is it possible to supply a vector?

EDIT:
Thank you Doc Al. That clears up the confusion for me
 
Last edited:
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The electric field is a vector. It has a direction, not a "charge". If the field points to the right, the force it exerts on a positive charge will be to the right.
 
x86 said:
An electric field has a force of x N/C and a charge of Y Coulombs is placed in the field.
The electric field doesn't have a force of ##x## N/C. Its magnitude is ##x## N/C. (I'm assuming here that ##x>0##.)

So, how can I determine the magnitude of the particle…?
The phrase "magnitude of the particle" makes no sense.

You seem to be confusing the electric charge with the electric field it produces.
 

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