Physics 1 hour

Introductory Physics Electrostatics Practice Problems Spring Semester

1. In the picture at the right, calculate the net force (magnitude and

direction) on 𝑞1.

2. Two objects separated by a distance of 1.75 m have charges +𝑄

and +3𝑄. A third charge 𝑞 is placed in-between the two positive

charges so they are all on a line. Where should 𝑞 be placed so that

it is in equilibrium with the other two charges? Give your answer

as a distance measured from charge +𝑄.

3. Three point charges are located on a circular arc (𝑟 = 3.80 cm) as

shown on the right. First find the electric force (magnitude and

direction) exerted on a −5.07 nC charge placed at position P. Then

remove that charge and find the total electric field (magnitude and

direction) at point P. (Adapted from Problem #26 in your book.)

4. Two charges (𝑞1 = +8.0 𝜇𝐶 and 𝑞2 = −3.0 𝜇𝐶) are separated by a distance of 1.0 m. Where along

the line connecting the two charges is the net electric field equal to zero? Give your answer as a

distance measured from 𝑞2.

5. Charge 𝑄1 = +50 𝜇𝐶 is positioned at 𝑥 = −26 cm, while charge 𝑄2 = −50 𝜇𝐶 is positioned at

𝑥 = +26 cm. What is the net electric field (magnitude and direction) at the xy-coordinate

(0, +30) cm?

Answers:

1) 23 N, 24° above +x; 2) 0.641 m; 3) 1.01 × 10−4 N to the left, 1.99 × 104 N/C to the right;

4) 1.6 m; 5) 3.7 × 106 N/C to the right

Question #1

Question #3