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

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

Question 1

Which of the following statements best describes the nature of electric charge?

Accepted Answer

Electric charge is a property of matter, not a substance itself.

Question 2

A plastic rod is rubbed with fur and then brought near small pieces of paper. The paper is attracted to the rod. Which phenomenon best explains this observation?

Accepted Answer

The paper is polarized by the electric field of the rod, resulting in attraction.

Question 3

Which of the following is true about the charges and masses of protons, neutrons, and electrons?

Accepted Answer

Neutrons have no charge and a mass similar to protons.

Question 4

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

Accepted Answer

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

Question 5

Which of the following best describes the difference between conductors and insulators?

Accepted Answer

Conductors have overlapping energy bands allowing free movement of electrons, while insulators have a large gap preventing free movement.

Question 6

A metal ball is initially uncharged. A negatively charged rod is brought near (but does not touch) the ball, and the ball is then grounded. What is the final charge on the ball after the ground and rod are removed?

Accepted Answer

The ball is positively charged.

Question 7

Which equation correctly expresses Coulomb's Law for the magnitude of the force between two point charges $$q_1$$ and $$q_2$$ separated by a distance $$r$$?

Accepted Answer

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

Question 8

Three charges are placed as shown: $$q_1 = 2$$\ \mu\mathrm{C}$$ at (0$$, 0.3)$$ m, q_2$ = 2\ \mu\mathrm{C} at$$ $$(-0.4, 0) m$$, and $$q_3 = 4$$\ \mu\mathrm{C}$$ at (0.4$$, 0)$$ m. What is the direction of the net force on q_3$?

Accepted Answer

Up and to the right (positive x and positive y direction)

Question 9

The electric field at a distance $$r$$ from a point charge $$Q is $$given by:

Accepted Answer

$$E = \frac{1}{4\pi\$$varepsilon_0$$} \frac{Q}{r^2$}$$

Question 10

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

Accepted Answer

$$\vec{p} = q \vec{d}$$

Question 11

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

Accepted Answer

The net force is zero.

Question 12

A charged particle of mass $$m$$ and charge $$q$$ enters a region with a uniform electric field $$E$$ between two parallel plates. If the particle enters with velocity $$v_0$$ parallel to the plates, what is the condition for the particle to pass through without hitting the plates (distance between plates is $$d$$, length of plates is $$L$$)?

Accepted Answer

$$v_0$$ \geq \sqrt{\frac{q E $$L^2$$}{2 m d}}$$

Question 13

What is the torque $$\vec{	au} on an $$electric dipole $$\vec{p} in a $$uniform electric field $$\vec{E}$$?

Accepted Answer

$$\vec{	au} = \vec{p} 	imes \vec{E}$$

Question 14

The potential energy $$U of an $$electric dipole in a uniform electric field $$\vec{E} is $$given by:

Accepted Answer

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

Question 15

What happens to the electric field $$E_z$$ along the axis of a uniformly charged disk of radius $$R$$ and surface charge density $$\sigma as$$ $$z 	o \infty$$?

Accepted Answer

$$E_z 	o 0$$

Question 16

Which of the following best describes the direction of electric field lines for a positive point charge?

Accepted Answer

They radiate outward from the charge.

Question 17

A comb is run through hair and then brought near small pieces of paper, which are attracted to the comb. What is the best explanation for this phenomenon?

Accepted Answer

The comb induces opposite charges on the paper, causing attraction.

Question 18

Which of the following is a correct statement about the superposition principle for electric fields?

Accepted Answer

The net electric field at a point is the vector sum of the electric fields from all charges.

Electric Charge and Electric Field: Foundations and Applications

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