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Physics C—Electricity and Magnetism Practice Exam 1—Multiple-Choice Questions ❮ 251
Physics C—Electricity and Magnetism Practice Exam 1—
Multiple-Choice Questions
ANSWER SHEET
1 A^ B^ C^ D^ E 2 A B C D E 3 A B C D E 4 A^ B^ C^ D^ E 5 A B C D E 13 A^ B^ C^ D^ E 14 A B C D E 15 A B C D E 16 A^ B^ C^ D^ E 17 A B C D E 25 A^ B^ C^ D^ E 26 A B C D E 27 A B C D E 28 A^ B^ C^ D^ E 29 A B C D E 6 A^ B^ C^ D^ E 7 A B C D E 8 A B C D E 9 A B C D E 10 A^ B^ C^ D^ E 18 A^ B^ C^ D^ E 19 A B C D E 20 A B C D E 21 A B C D E 22 A^ B^ C^ D^ E 30 A^ B^ C^ D^ E 31 A B C D E 32 A B C D E 33 A B C D E 34 A^ B^ C^ D^ E 11 A B C D E 12 A^ B^ C^ D^ E 23 A B C D E 24 A^ B^ C^ D^ E 35 A B C D E
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254 ❯ STEP 5. Build Your Test-Taking Confidence
30 ° E
- A uniform electric field points to the left. A small metal ball charged to −2 mC hangs at a 30° angle from a string of negligible mass, as shown above. The tension in the string is measured to be 0.1 N. What is the magnitude of the electric field? (sin 30° = 0.50; cos 30° = 0.87; tan 30° = 0.58.) (A) 25 N/C (B) 50 N/C (C) 2,500 N/C (D) 5,000 N/C (E) 10,000 N/C
- A thin semicircular conductor of radius R holds charge +Q. What is the magnitude and direction of the electric field at the center of the circle? (A) kQ R 2
(B)
kQ R 2
(C)
π kQ R^2
(D)
π kQ R^2
(E) The electric field is zero at the center.
- Above an infinitely large plane carrying charge density s, the electric field points up and is equal to s/2eo. What is the magnitude and direction of the electric field below the plane? (A) s/2eo, down (B) s/2eo, up (C) s/eo, down (D) s/eo, up (E) zero 2 a a^ a .A .B .E . C .D
- Three charges are arranged in an equilateral tri- angle, as shown above. At which of these points is the electric potential smallest? (A) A (B) B (C) C (D) D (E) E
Physics C—Electricity and Magnetism Practice Exam 1—Multiple-Choice Questions ❮ 255
10V 40V 70V Point P
- The diagram shows a set of equipotential surfaces. At point P, what is the direction of the electric field? (A) left (B) right (C) up the page (D) down the page (E) either left or right, which one cannot be determined
- A metal sphere carries charge Q; a noncon- ducting sphere of equal size carries the same charge Q, uniformly distributed throughout the sphere. These spheres are isolated from each other. Consider the electric field at the center of the spheres, within the spheres, and outside the spheres. Which of these electric fields will be the same for both spheres, and which will be different? Elsewhere At the Within the Outside Center Sphere the Sphere (A) Same Same Same (B) Same Same Different (C) Same Different Same (D) Different Different Same (E) Different Different Different
- Under what conditions is the net electric flux through a closed surface proportional to the enclosed charge? (A) under any conditions (B) only when the enclosed charge is symmetrically distributed (C) only when all nearby charges are symmetrically distributed (D) only when there are no charges outside the surface (E) only when enclosed charges can be considered to be point charges radius r axis
- A hollow metal ring of radius r carries charge q. Consider an axis straight through the center of the ring. At what point(s) along this axis is/are the electric field equal to zero? (A) only at the center of the ring (B) only at the center of the ring, and a very long distance away (C) only a very long distance away (D) only at the center of the ring, a distance r away from the center, and a very long distance away (E) everywhere along this axis a c b
- A parallel plate capacitor consists of identical rectangular plates of dimensions a × b, separated by a distance c. To cut the capacitance of this capacitor in half, which of these quantities should be doubled? (A) a (B) b (C) c (D) ab (E) abc
- Two identical capacitors are hooked in parallel to an external circuit. Which of the following quantities must be the same for both capacitors? I. the charge stored on the capacitor II. the voltage across the capacitor III. the capacitance of the capacitor (A) I only (B) II only (C) II and III only (D) I and III only (E) I, II, and III
Physics C—Electricity and Magnetism Practice Exam 1—Multiple-Choice Questions ❮ 257
- A uniform magnetic field B is directed into the page. An electron enters this field with initial velocity v to the right. Which of the following best describes the path of the electron while it is still within the magnetic field? (A) It moves in a straight line. (B) It bends upward in a parabolic path. (C) It bends downward in a parabolic path. (D) It bends upward in a circular path. (E) It bends downward in a circular path.
P
I
I
r 2
r 1 r
3
- Wire is wound around an insulated circular donut, as shown above. A current I flows in the wire in the direction indicated by the arrows. The inner, average, and outer radii of the donut are indicated by r 1 , r 2 , and r 3 , respectively. What is the magnitude and direction of the magnetic field at point P, the center of the donut? (A) zero (B) μ I 2 r o 1 (C)^ μ^ I 2 r o 2 (D) μ I 2 r o 3 (E) μ π
I
2 r o 2
I
e-
- A wire carries a current toward the top of the page. An electron is located to the right of the wire, as shown above. In which direction should the electron be moving if it is to experience a magnetic force toward the wire? (A) into the page (B) out of the page (C) toward the bottom of the page (D) toward the top of the page (E) to the right
- Which of the following statements about electric and magnetic fields is FALSE: (A) A charge moving along the direction of an electric field will experience a force, but a charge moving along the direction of a magnetic field will not experience a force. (B) All charges experience a force in an electric field, but only moving charges can experience a force in a magnetic field. (C) A positive charge moves in the direction of an electric field; a positive charge moves per- pendicular to a magnetic field. (D) All moving charges experience a force paral- lel to an electric field and perpendicular to a magnetic field. (E) A negative charge experiences a force oppo- site the direction of an electric field; a nega- tive charge experiences a force perpendicular to a magnetic field.
- Which of these quantities decreases as the inverse square of distance for distances far from the objects producing the fields? (A) the electric field produced by a finite-length charged rod (B) the electric field produced by an infinitely long charged cylinder (C) the electric field produced by an infinite plane of charge (D) the magnetic field produced by an infinitely long, straight current-carrying wire (E) the magnetic field produced by a wire curled around a torus
258 ❯ STEP 5. Build Your Test-Taking Confidence
- A proton enters a solenoid. Upon entry, the proton is moving in a straight line along the axis of the sole- noid. Which of the following is a correct descrip- tion of the proton’s motion within the solenoid? (A) The proton will be bent in a parabolic path. (B) The proton will be bent in a circular path. (C) The proton will continue in its straight path at constant velocity. (D) The proton will continue in its straight path and slow down. (E) The proton will continue in its straight path and speed up.
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
A X
C
B
B 'eld
- A uniform magnetic field points into the page. Three subatomic particles are shot into the field from the left-hand side of the page. All have the same initial speed and direction. These particles take paths A, B, and C, as labeled in the diagram above. Which of the following is a possible identity for each particle? A B C (A) antiproton proton electron (B) antiproton positron neutron (C) proton electron neutron (D) positron antiproton neutron (E) electron proton neutron
v
v
B out
of page
- The electric dipole shown above consists of equal-magnitude charges and has an initial left- ward velocity v in a uniform magnetic field pointing out of the page, as shown above. The dipole experiences (A) a clockwise net torque, and a net force to the left (B) a counterclockwise net torque, and a net force to the left (C) no net torque, and a net force to the left (D) a counterclockwise net torque, and no net force (E) a clockwise net torque, and no net force
- A beam of electrons has speed 10^7 m/s. It is desired to use the magnetic field of the Earth, 5 × 10 −^5 T, to bend the electron beam into a circle. What will be the radius of this circle? (A) 1 nm (B) 1 μm (C) 1 mm (D) 1 m (E) 1 km I dL P
- A very small element of wire of length dL carries a current I. What is the direction of the magnetic field produced by this current element at point P, shown above? (A) to the right (B) toward the top of the page (C) into the page (D) out of the page (E) there is no magnetic field produced at point P by this element.
260 ❯ STEP 5. Build Your Test-Taking Confidence
R 2
R 1
L
I
10 V
- If the two equal resistors R 1 and R 2 are connected in parallel to a 10-V battery with no other circuit components, the current provided by the battery is I. In the circuit shown above, an inductor of inductance L is included in series with R 2. What is the current through R 2 after the circuit has been connected for a long time? (A) zero (B) (1/4) I (C) (1/2) I (D) I (E)
I
R R
LR
1 2 2 STOP. End of Physics C—Electricity and Magnetism Practice Exam 1—Multiple-Choice Questions
Physics C—Electricity and Magnetism Practice Exam 1—Free-Response Questions ❮ 261
Physics C—Electricity and Magnetism Practice Exam 1—
Free-Response Questions
Time: 45 minutes. You may refer to the constants sheet and the equation sheet, both of which are found in the appendix. You may use a calculator.
E&M 1
+2Q +Q R 1 R 2 R 3 A metal sphere of radius R 1 carries charge +Q. A concentric spherical metal shell, of inner radius R 2 and outer radius R 3 , carries charge + 2 Q. (a) Let r represent the distance from the center of the spheres. Calculate the electric field as a function of r in each of the following four regions:
- between r = 0 and r = R 1
- between r = R 1 and r = R 2
- between r = R 2 and r = R 3
- between r = R 3 and r = 0 (b) How much charge is on each surface of the outer spherical shell? Justify your answer. (c) Determine the electric potential of the outer spherical shell. (d) Determine the electric potential of the inner metal sphere.
Physics C—Electricity and Magnetism Practice Exam 1—Free-Response Questions ❮ 263
E&M 3
In the laboratory, far from the influence of other magnetic fields, the Earth’s magnetic field has a value of 5.00 × 10 −^5 T. A compass in this lab reads due north when pointing along the direction of Earth’s magnetic field. S W E N 340 0 320 30 0 28 0 260 24 0 22 0 020 016 14 0 12 0 10 0 80 60 40 20 48° 180 A long, straight current-carrying wire is brought close to the compass, deflecting the compass to the position shown above, 48° west of north. (a) Describe one possible orientation of the wire and the current it carries that would produce the deflection shown. (b) Calculate the magnitude Bwire of the magnetic field produced by the wire that would cause the deflection shown. (c) The distance d from the wire to the compass is varied, while the current in the wire is kept constant; a graph of Bwire vs. d is produced. On the axes below, sketch the shape of this graph. B d (d) It is desired to adjust this plot so that the graph becomes a straight line. The vertical axis is to remain Bwire, the magnetic field produced by the wire. How could the quantity graphed on the horizontal axis be adjusted to produce a straight-line graph? Justify your answer. (e) The current carried by the wire is 500 mA. Determine the slope of the line on the graph suggested in part (d). STOP. End of Physics C—Electricity and Magnetism Practice Exam 1—Free-Response Questions
