**#11**

Three charges are at the corners of an equilateral triangle, as shown in the figure below. Calculate the electric field at a point midway between the two charges on the *x*-axis. (Let *q*_{1} = 7.00 *μ*C,

*q*_{2} = 9.00 *μ*C,

and *q*_{3} = −3.00 *μ*C.)

Three charged particles lie in the *x* *y*-coordinate plane at the vertices of an equilateral triangle with side length 0.500 m.

- Positive charge
*q*_{2}is at the origin. - Positive charge
*q*_{1}is in the first quadrant, along a line 60.0°counterclockwise from the positive*x*-axis. - Negative charge
*q*_{3}is at (0.500, 0).

Magnitude__________N/C

Direction_________° below the +*x*-axis

**#12**

Three identical charges (*q* = −7.2 *μ*C)

lie along a circle of radius 3.3 m at angles of 30°, 150°, and 270°, as shown in the figure below. What is the resultant electric field at the center of the circle?

Three negative point charges are located on the circumference of a circle of radius *r* centered on the origin of the *x* *y*-plane. Each point charge is labeled *q*. The charges are located at the following angular positions along the circumference.

- 30° counterclockwise from the +
*x*-axis - 150° counterclockwise from the +
*x*-axis - 270° counterclockwise from the +
*x*-axis

__________ N/C