Q: A neutral lithium atom has 3 protons, 4 neutrons, and 3 electrons. If one electron is removed, what is the resulting net charge of the ion?

$$+1.6 \times 10$$^{-19}$$\ \mathrm{C}$$

Question 1

Which of the following statements best explains why water is such a good solvent for ionic compounds like NaCl?

Accepted Answer

Water molecules are electric dipoles, so their positive and negative ends attract and stabilize ions.

Question 2

Which of the following is the correct expression for the electric force between two point charges $$q_1$$ and $$q_2$$ separated by a distance $$r in $$vacuum?

Accepted Answer

$$F = k \frac{q_1$ q_2$}{r^2$}$$

Question 3

A neutral lithium atom has 3 protons, 4 neutrons, and 3 electrons. If one electron is removed, what is the resulting net charge of the ion?

Accepted Answer

$$+1.6 	imes 10$$^{-19}$$\ \mathrm{C}$$

Question 4

Which of the following best describes the direction of the electric field produced by a negative point charge?

Accepted Answer

Radially inward toward the charge

Question 5

The SI unit of electric charge is the:

Accepted Answer

Coulomb (C)

Question 6

If three point charges are placed at the corners of a triangle, how is the net force on one charge determined?

Accepted Answer

By vectorially summing the forces from the other two charges

Question 7

Which of the following is the correct formula for the electric field $$\vec{E} at a $$distance $$r$$ from a point charge $$Q$$?

Accepted Answer

$$\vec{E} = k \frac{Q}{r^2$} \hat{r}$$

Question 8

A dipole consists of charges $$+q$$ and $$-q$$ separated by a distance $$d. $$What is the direction of the dipole moment vector $$\vec{p}$$?

Accepted Answer

From $$-q to$$ $$+q$$

Question 9

What is the net force on an electric dipole placed in a uniform electric field?

Accepted Answer

Zero

Question 10

Which of the following best describes the potential energy $$U of an $$electric dipole with dipole moment $$\vec{p} in a $$uniform electric field $$\vec{E}$$?

Accepted Answer

$$U = -\vec{p} \cdot \vec{E}$$

Question 11

A charge distribution has a volume charge density $$\rho. $$Which of the following integrals gives the total charge $$Q in a $$volume $$V$$?

Accepted Answer

$$Q = \int_V \rho\ dV$$

Question 12

Which of the following is true about electric field lines?

Accepted Answer

They indicate the direction of the electric field at each point.

Question 13

A neutral atom is placed in an external electric field. What is the net force on the atom, and what effect does the field have?

Accepted Answer

The net force is zero, but the atom becomes polarized.

Question 14

Which of the following best describes the superposition principle for electric fields?

Accepted Answer

The total electric field is the vector sum of the fields due to individual charges.

Question 15

If the distance between two point charges is doubled, what happens to the magnitude of the electric force between them?

Accepted Answer

It becomes one-fourth as large.

Question 16

Which of the following is the correct expression for the torque $$	au on an $$electric dipole in a uniform electric field $$E$$?

Accepted Answer

$$	au = pE \sin 	heta$$

Question 17

A surface charge density $$\sigma is $$defined as:

Accepted Answer

$$\sigma = \frac{dq}{dA}$$

Question 18

Which of the following is NOT a property of electric field lines?

Accepted Answer

They form closed loops.

Electric Charge and Electric Field: Foundations of Electrostatics

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