An electron moves from point i to point f, in the direction of a uniform electric field. During this motion:Group of answer choicesthe work done by the field is positive and the potential energy of the electron-field system increasesthe work done by the field is negative and the potential energy of the electron-field system increasesthe work done by the field is positive and the potential energy of the electron-field system decreasesthe work done by the field is negative and the potential energy of the electron-field system decreasesthe work done by the field is positive and the potential energy of the electron-field system does not change

the work done by the field is positive and the potential energy of the electron field system decreases

Explanation:

This exercise asks to find the work and the potential energy of an electron in an electric field.

Work is defined by

         W = F .d = F d cos θ

the electric force is

          F_e = q E

         W = q E d cos θ

since the charge of the electron is negative the force is in the opposite direction to the electric field

          W = - e E d

we select the direction to the right is positive, point i is to the left of point f,

therefore the work moving from point i to point F has two possibilities

* The electric field lines go from i to f point , so that point i is on the side of the positive charges, so the electron approaches them, This movement is opposite to that indicated

* the field line reaches point i, this implies that the charges are negative, so the electrioc field is then negativeand the electron charge is negative too.  The electron moves away from this point, this is in accordance with the indicated movement

In the latter case the electric field lines go from f to i point, therefore the Work is positive

Now let's examine the potential energy

            ΔU = - q E .d

so we see that this definition is related to work,

            ΔU = -W

Therefore, as the work is positive, the power energy must decrease

When reviewing the different answers, the correct ones are:

the work done by the field is positive and the potential energy of the electron field system decreases

hi there!

out of the two, (b) precision would be more reasonable.   however, both a and b could be pretty reasonable.

-awesomerepublic   : )

cant without the picture! ?