Question

Consider the electric field diagram above.

a. Points A, B, and C are all located at y = 0.06 m .

i. At which of these three points is the magnitude of the electric field the greatest? Justify your answer.

ii. At which of these three points is the electric potential the greatest? Justify your answer.

b. An electron is released from rest at point B.

i. Qualitatively describe the electron's motion in terms of direction, speed, and acceleration.

ii. Calculate the electron's speed after it has moved through a potential difference of 10 V.

c. Points B and C are separated by a potential difference of 20 V. Estimate the magnitude of the electric field midway between them and state any assumptions that you make.

d. On the diagram, draw an equipotential line that passes through point D and intersects at least three electric field lines.

Answer 1

a. i. The magnitude of the field is greatest at point C because this is where the field lines are closest together.

ii. The potential is greatest at point A. Electric field lines point from high to low potential.

b. i. The electron moves to the left, against the field lines. As the field gets weaker the electron’s acceleration to the left decreases in magnitude, all the while gaining speed to the left.

ii. W = qΔV = ½ mv² gives v = 1.9 × 10⁶ m/s

c. If we assume the field is nearly uniform between B and C we can use E = ΔV/d where the distance between B and C d = 0.01 m giving E = 20 V/0.01 m = 2000 V/m

d.