A very long, straight wire has charge per unit length $3.20\times {10}^{-10}$ C/m. At what distance from the wire is the electric field magnitude equal to $2.50$ N/C?

A point charge $q_1=-4.00$ nC is at the point $x=0.600$ m, $y=0.800$ m, and a second point charge $q_2=+6.00$ nC is at the point $x=0.600$ m, $y=0$. Calculate the magnitude and direction of the net electric field at the origin due to these two point charges.

A point charge is placed at each corner of a square with side length $a$. All charges have magnitude $q$. Two of the charges are positive and two are negative (Fig. E$21.42$). What is the direction of the net electric field at the center of the square due to the four charges, and what is its magnitude in terms of $q$ and $a$?

Point charges $q_1=-4.5$ nC and $q_2=+4.5$ nC are separated by $3.1$ mm, forming an electric dipole. The charges are in a uniform electric field whose direction makes an angle of $36.9$° with the line connecting the charges. What is the magnitude of this field if the torque exerted on the dipole has magnitude $7.2\times {10}^{-9}$ Nm?

An electric dipole with dipole moment $p$ is in a uniform external electric field $E$. Find the orientations of the dipole for which the torque on the dipole is zero.

An electric dipole with dipole moment $p$ is in a uniform external electric field $E$. Which of the orientations in part (a) is stable, and which is unstable? (Hint: Consider a small rotation away from the equilibrium position and see what happens.) Note: Part (a) asked to find the orientations of the dipole for which the torque on the dipole is zero.

A $-4.00$-nC point charge is at the origin, and a second $-5.00$-nC point charge is on the $x$-axis at $x = 0.800$ m. Find the net electric force that the two charges would exert on an electron placed at each point in part (a). Note: Part (a) asked to find the electric field (magnitude and direction) at each of the following points on the $x$-axis: (i) $x = 0.200$ m; (ii) $x = 1.20$ m; (iii) $x = -0.200$ m.