Concept #1: Work due to Electric Force

Practice: An electron moves from point A to point B. The potential difference between these two points is 100 V. What is

a. the point of higher potential?

b. the work done on the electron?

c. the final speed of the electron if its initial speed is zero?

Example #1: Work to Bring Two Charges From Infinity

Practice: What work is needed to assemble an equilateral triangle of side length 5 cm, with a 5uC charge at each vertex?

Example #2: Speed of Electron in Electric Field

Two point charges q1 = +10.00 nC and q 2 = +2.00 nC are 0.100 m apart as shown in the figure to the right. Point A is midway between q1 and q2. Point B is 0.080 m from q 1 and 0.060 from q 2. Determine the energy required to move a charge q 3 = +10.00 nC from point B to point A.

Three point charges, each of magnitude q, are placed at 3 corners of a square with sides of length L as shown. How much work is required to bring a test charge Q from very far away to A along the indicated path direction?

A -3 μC point charge and a -9 μC point charge are initially extremely far apart. How much work does it take to bring the -3 μC charge to x = 3 mm, y = 0 mm and the -9 μC charge to x = -3 mm and y = 0 mm?
a. 40 J
b. 81 J
c. 27 J
d. 6.8 J

Consider a square with sides L = 48cm and two negative charges Q = - 2.5 μC placed on the corners labeled with Q in the figure. How much work is required to bring an electron from very far away to the corner of the square labeled by B?

A uniform electric field, with a magnitude of 15 x10 2 N/C, is directed parallel to the positive x-axis. The work done by the electron as it moves from A (x = 2 m) to B (x = 7 m) is -3.2 x 10-16 J. If potential at A is +5000 V, what is the potential at B? (For an electron q = -1.6 x 10 -19 C)
(a) -2800 V
(b) +3000 V
(c) +7000 V
(d) -2000 V

The two charges Q are fixed at the vertices of an equilateral triangle with sides of length a as shown.The work required to move a charge q from the other vertex to the center of the line joining the fixed charges is1. W = √ 2kQq / a2. W = 03. W = 2kQq / a4. W = 4kQq / a5. W = kQq / a6. W = 6kQq / a

Through what potential difference would an electron need to be accelerated for it to achieve a speed of 2.4 % of the speed of light (2.99792×108 m/s), starting from rest?

A 3.0 μC negative charge is attracted to a large, well-anchored, positive charge. How much kinetic energy does the negatively charged object gain if the potential difference through which it moves is 4 mV?A) 1.33 kJB) 1.33 JC) 3.0 μJD) 12 nJ

Two point charges +9.0 μC are affixed at the corners of the base of an equilateral triangle, as shown in the figure. A third charge +3.3 μC is first placed midway between two charges at point (a). Find the work done by the two charges as it moves from point (a) to (b). (k = 1/4πε0 = 8.99 x 109 N•m2/C2).