Direction of Electric Force in a E. Field?

  • #1
Member warned to use the template.
Is the electric force negative when it is in opposite direction as the electric field? If it is, a positive charge would always have a positive E. force? thanks.

Answers and Replies

  • #2
Homework Helper
Gold Member
Hello K.z_z and welcome to PF!

Force and electric fields are vectors. The best way to specify a vector quantity is to give the magnitude of the vector and the direction of the vector. The magnitude is always a positive number. In general, there are an infinite number of possible directions that a vector can point in 3 dimensional space (or 2 dimensional space). So, saying that a vector is "positive" or "negative" does not usually have much meaning. Sometimes a vector points in, say, the positive x direction of some coordinate system, and then you can just say that the direction of the vector is "in the positive x direction". But, in general, a vector will point in some direction that cannot be specified by saying that the vector is "positive" or "negative".

For example, suppose you have an electric field that lies in the x-y plane and points in a direction of 30 degrees counterclockwise from the positive x axis. If you place a negative charge in this field, then the force would be in the opposite direction to the electric field. So, you could specify the direction of the force as 210 degrees counterclockwise from the positive x axis (or, equivalently, 30 degrees below the negative x axis, etc.) But giving the direction of the force by saying that it is "a negative force" would not be a valid way of describing the force.