Q: A small piece of aluminum contains $$10^{23}$$ atoms. If it has a net positive charge of $$3.0\ \mu\mathrm{C}$$, what fraction of its electrons has it lost? (Charge of electron $$e = 1.6 \times 10$$^{-19}$$\ \mathrm{C})$$

$$\frac{3.0 \times 10$$^{-6}$$}{10$$^{23}$$ \times 1.6 \times 10$$^{-19}$$} = 1.9 \times 10$$^{-4}$$

Q: A negative charge of mass $$0.1\ \mathrm{kg}$$ and charge $$0.1\ \mu\mathrm{C} is $$suspended in a uniform electric field such that the electric force cancels gravity. What is the required electric field strength?

$$E = \frac{mg}{q} = \frac{0.1 \times 9.8}{0.1 \times 10$$^{-6}$$} = 9.8 \times 10$$^{6}$$\ \mathrm{N/C}$$

Question 1

Which of the following statements best describes the difference between conductors and insulators at the atomic level?

Accepted Answer

Conductors have atoms with loosely bound electrons that can move freely, while insulators have tightly bound electrons that cannot move freely.

Question 2

A neutral aluminum sphere is brought into contact with a negatively charged rod. What happens to the aluminum sphere?

Accepted Answer

It gains electrons and becomes negatively charged.

Question 3

Which of the following is the correct mathematical expression for 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 4

Two identical conducting spheres, one with charge $$+5\ \mu\mathrm{C}$$ and the other with $$-1\ \mu\mathrm{C}$$, are brought into contact and then separated. What is the final charge on each sphere?

Accepted Answer

$$+2\ \mu\mathrm{C}$$

Question 5

A small piece of aluminum contains $$10^{23}$$ atoms. If it has a net positive charge of $$3.0\ \mu\mathrm{C}$$, what fraction of its electrons has it lost? (Charge of electron $$e = 1.6 	imes 10$$^{-19}$$\ \mathrm{C})$$

Accepted Answer

$$\frac{3.0 	imes 10$$^{-6}$$}{10$$^{23}$$ 	imes 1.6 	imes 10$$^{-19}$$} = 1.9 	imes 10$$^{-4}$$

Question 6

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

Accepted Answer

It points radially outward from the charge.

Question 7

A negative charge of mass $$0.1\ \mathrm{kg}$$ and charge $$0.1\ \mu\mathrm{C} is $$suspended in a uniform electric field such that the electric force cancels gravity. What is the required electric field strength?

Accepted Answer

$$E = \frac{mg}{q} = \frac{0.1 	imes 9.8}{0.1 	imes 10$$^{-6}$$} = 9.8 	imes 10$$^{6}$$\ \mathrm{N/C}$$

Question 8

Which of the following is true about the electric field inside a conductor in electrostatic equilibrium?

Accepted Answer

The electric field is zero.

Question 9

A parallel plate capacitor has a plate separation $$d$$ and a potential difference $$V$$ between the plates. What is the magnitude of the electric field between the plates?

Accepted Answer

$$E = \frac{V}{d}$$

Question 10

Which of the following best describes the concept of electric flux through a surface?

Accepted Answer

It is the number of electric field lines crossing a surface, proportional to $$EA\cos	heta.$$

Question 11

According to Gauss's Law, the net electric flux through a closed surface is proportional to:

Accepted Answer

The total charge enclosed by the surface.

Question 12

A $$+1.0\ \mathrm{C}$$ charge and a $$-4.0\ \mathrm{C}$$ charge are $$2.0\ \mathrm{m}$$ apart. What is the magnitude of the electric field at the point midway between them?

Accepted Answer

$$E = k \left| \frac{1.0}{1.0^2$} - \frac{4.0}{1.0^2$} \right|$$

Question 13

Which of the following is a correct statement about the behavior of charges on a conductor?

Accepted Answer

Charges reside only on the surface of the conductor.

Question 14

A thunderstorm has a $$+50\ \mathrm{C}$$ charge at the top of a cloud $$10\ \mathrm{km}$$ above the Earth's surface and a $$-20\ \mathrm{C}$$ charge at the bottom $$2\ \mathrm{km}$$ above the surface. What is the sign of the induced charge on the Earth's surface directly below the cloud?

Accepted Answer

Positive

Question 15

Which of the following best explains why the electric field is perpendicular to the surface of a conductor in electrostatic equilibrium?

Accepted Answer

Because any parallel component would cause charges to move, violating equilibrium.

Question 16

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

Accepted Answer

It is reduced to one-fourth.

Question 17

Which of the following is the correct expression for the electric field $$E$$ due to a point charge $$q at a $$distance $$r$$?

Accepted Answer

$$E = k \frac{q}{r^2$}$$

Question 18

A charged rod is brought near a neutral soda can (a conductor). What happens to the soda can?

Accepted Answer

It is attracted regardless of the rod's charge.

Question 19

Which of the following is a correct application of the principle of superposition in electrostatics?

Accepted Answer

The net electric field at a point is the vector sum of the fields from each charge.

Electric Charge and Electric Field – Physics 202 (Giancoli Ch 16) Study Notes

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