Q: A dipole in a $$300\ \mathrm{V/m}$$ electric field is initially perpendicular to the field. The dipole rotates so its axis is in the same direction as the field. If the magnitude of the dipole moment is $$2 \times 10$$^{-7}$$\ \mathrm{C\cdot m}$$, the work done on the dipole is:

$$6 \times 10$$^{-5}$$\ \mathrm{J}$$

Q: A long, thin rod parallel to the $$y-$$axis is located at $$x=-1.0\ \mathrm{cm}$$ and carries a uniform linear charge density of $$+1.0\ \mathrm{nC/m}. A $$second long, thin rod parallel to the $$z-$$axis is located at $$x=+1.0\ \mathrm{cm}$$ and carries a uniform linear charge density of $$-1.0\ \mathrm{nC/m}. $$What is the net electric field due to these rods at the origin?

$$(-1.8 \times 10^4$)\ \mathrm{N/C}\ \hat{i}$$

Q: Total charge $$Q = -820\ \mathrm{nC} is $$uniformly distributed on a ring of $$2.4\ \mathrm{m}$$ radius. A point charge $$q = +530\ \mathrm{nC} is $$fixed at the center of the ring. Points $$A$$ and $$B$$ are located on the axis of the ring, as shown in the figure below. What is the work that an external force must do to transport an electron from $$B to$$ $$A$$?

$$+8.7 \times 10$$^{-17}$$\ \mathrm{J}$$

Question 1

A charge $$q is $$placed at the center of a sphere of radius $$1.0\ \mathrm{m}. $$What happens to the total electric flux through the surface of the sphere when the radius is changed to $$0.5\ \mathrm{m}$$?

Accepted Answer

The flux remains the same and the field increases.

Question 2

If the net electric flux through a Gaussian surface is zero, which of the following statements must be true?

Accepted Answer

The number of electric field lines entering the surface equals the number leaving the surface.

Question 3

A charged parallel plate capacitor is removed from the battery and the plates are pushed apart to a larger separation. Assume that no electric charge is lost in the process. Which of the following quantities increases?

Accepted Answer

The energy stored in the capacitor.

Question 4

A dipole in a $$300\ \mathrm{V/m}$$ electric field is initially perpendicular to the field. The dipole rotates so its axis is in the same direction as the field. If the magnitude of the dipole moment is $$2 	imes 10$$^{-7}$$\ \mathrm{C\cdot m}$$, the work done on the dipole is:

Accepted Answer

$$6 	imes 10$$^{-5}$$\ \mathrm{J}$$

Question 5

The household voltage in Hong Kong is $$220\ \mathrm{V}. $$The resistance of a $$100\ \mathrm{W}$$ light bulb designed for domestic use in Hong Kong is:

Accepted Answer

$$484\ \Omega$$

Question 6

Two identical conducting spheres $$A$$ and $$B$$ carry equal charge. They are separated by a distance much larger than their diameters. A third identical conducting sphere $$C is $$uncharged. Sphere $$C is $$first in contact with $$A$$, then with $$B$$, and finally removed. As a result, the electrostatic force between $$A$$ and $$B$$, which was originally $$F$$, becomes:

Accepted Answer

$$F/4$$

Question 7

Charge $$Q is $$distributed uniformly on the surface of a spherical balloon (an insulator). A point particle with charge $$q is $$inside. The electric field at the center of the balloon is:

Accepted Answer

It is always zero at the balloon center.

Question 8

A metal cylinder of radius $$2.0\ \mathrm{mm} is $$concentric with another metal cylinder of radius $$5.0\ \mathrm{mm}. If $$the space between the cylinders is filled with air and the length of the cylinders is $$50\ \mathrm{cm}$$, what is the capacitance of this arrangement?

Accepted Answer

$$60\ \mathrm{pF}$$

Question 9

A battery of voltage $$9\ \mathrm{V} is $$used to charge a capacitor with capacitance $$2\ \mu\mathrm{F} by $$simply connecting the two terminals of the battery to that of the capacitor with electric wires. After reaching equilibrium, the total charge on the capacitor is $$Q=\underline{\hspace{1cm}}\ \mu\mathrm{C}.$$

Accepted Answer

$$162$$

Question 10

A battery of voltage $$9\ \mathrm{V} is $$used to charge a capacitor with capacitance $$2\ \mu\mathrm{F} by $$simply connecting the two terminals of the battery to that of the capacitor with electric wires. After reaching equilibrium, the energy stored in the capacitor is $$U=\underline{\hspace{1cm}}\ \mu\mathrm{J}.$$

Accepted Answer

$$81$$

Question 11

A long, thin rod parallel to the $$y-$$axis is located at $$x=-1.0\ \mathrm{cm}$$ and carries a uniform linear charge density of $$+1.0\ \mathrm{nC/m}. A $$second long, thin rod parallel to the $$z-$$axis is located at $$x=+1.0\ \mathrm{cm}$$ and carries a uniform linear charge density of $$-1.0\ \mathrm{nC/m}. $$What is the net electric field due to these rods at the origin?

Accepted Answer

$$(-1.8 	imes 10^4$)\ \mathrm{N/C}\ \hat{i}$$

Question 12

A $$2.0\ \mathrm{mm}$$ thick slab of $$2.0\ \mathrm{m}$$ has a charge of $$8.0 	imes 10$$^{-7}$$\ \mathrm{C}$$ distributed uniformly throughout its volume. Point $$P is $$located within the slab beneath its center, $$1.0\ \mathrm{mm}$$ from one of the faces. What is the electric field at $$P$$?

Accepted Answer

$$34\ \mathrm{N/C}$$

Question 13

A capacitor in the figure below is charged with a constant current $$I$$ during a period $$\Delta t. At $$the point $$P$$ between the plates, there is:

Accepted Answer

A changing electric field.

Question 14

Each of the four batteries shown below has an emf of $$3.0\ \mathrm{V}$$ and a $$1.0\ \Omega$$ internal resistance. Find the current through the $$3.0\ \Omega$$ resistor.

Accepted Answer

$$1.5\ \mathrm{A}$$

Question 15

A large negatively charged object is placed on an insulating table. A neutral metallic ball rolls straight towards the object but stops before touching it. A second neutral metallic ball rolls up along the same path as the first ball, lightly hits the first ball and rebounds, while driving the first ball a bit closer to the negatively charged object. After both balls have stopped rolling, the first ball is closer to the negatively charged object than is the second ball. At no time did either ball touch the charged object. Which statement is correct concerning the final charge on each ball?

Accepted Answer

The first ball is positive and the second negative.

Question 16

Total charge $$Q = -820\ \mathrm{nC} is $$uniformly distributed on a ring of $$2.4\ \mathrm{m}$$ radius. A point charge $$q = +530\ \mathrm{nC} is $$fixed at the center of the ring. Points $$A$$ and $$B$$ are located on the axis of the ring, as shown in the figure below. What is the work that an external force must do to transport an electron from $$B to$$ $$A$$?

Accepted Answer

$$+8.7 	imes 10$$^{-17}$$\ \mathrm{J}$$

Question 17

A $$2\ \mu\mathrm{F}$$ capacitor is connected across an ideal $$15\ \mathrm{V} DC $$battery. What is the current in the circuit when the capacitor has reached $$12\% of $$its maximum charge?

Accepted Answer

$$4.81\ \mu\mathrm{A}$$

Question 18

A potential difference $$V_{ab} = 120\ \mathrm{V} is $$applied between points $$a$$ and $$b. $$After the network is assembled, switch $$S_1 is $$closed for a long time, but switch $$S_2 is $$kept open. Then switch $$S_1 is $$opened and switch $$S_2 is $$closed. What is the final voltage across capacitor $$X$$?

Accepted Answer

$$100\ \mathrm{V}$$

Electrostatics and Capacitance: College Physics Study Guide

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