# electric field and force, direction of test charge?

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#### amar21

##### professional crammer
10+ Year Member
7+ Year Member
From what I gathered its like this... (hypothetical situations)

If my electric field is positive, it looks like this .. -----------> +, now, if I apply a negative force to the field, that force will in the opposite direction of the + field, where as a positive force will move in the same direction as the field

Is that right??

#### Bu2009

##### Full Member
10+ Year Member
This what I took away from studying this section.

The electric field is a vector field, at each of the points surrounding the source charge (which we assume to be positive) we assign a specific vector. This vector tells us teh magnitude, of the field at that point. Direction of the vector tells the direction of the resulting electric force that a positive test charge would feel.

This is from TPR book.

Due to this convention of assigning source charge as positive, electric field vectors always point away from positive source charges and toward negative ones.

So in your case you said that a negative force is applied. Based on the formula F (on q) = qE.(q) = charge E = electric field, F = Electric force, we see that if we apply (negative force) -F on q = -qE, the electric field and the force would both be in the same direction if we take our charge to be positive, but if the charge is negative, -(-qE), the Electric field would run the opposite as the Electric force. This is just convention that the charge is positive, if the charge is negative, you can see that when a negative force is applied on a negative charge, the resulting electric field line will be positive, signifying opposite direction as the negative force -F = -(-qE) = +qE.

well this is my take on it, but my logic might be flawed. I would some input from some SDN experts, physics pros at this at well

thanks

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#### futuredoctor10

##### Full Member
10+ Year Member
"Electric field vectors always point toward negative charges and away from positive charges."

Yep. From Intro Physics and MCAT books, I believe this to be correct and what we should know to do any MCAT problems