MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.

Transcription

1 Exam Name MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the 1) A small sphere with a mass of 441 g is moving upward along the vertical +y-axis when it encounters an electric field of 5.00 N/C i^. If, due to this field, the sphere suddenly acquires a horizontal acceleration of 13.0 m/s 2 i^, what is the charge that it carries? A) 1150 C B) 1.15 C C) C D) C 2) A dipole with a positive charge of 2.0 µc and a negative charge of -2.0 µc is centered at the origin and oriented along the x-axis with the positive charge located to the right of the origin. The charge separation is m. Find the electric field due to this dipole at the point x = 4.0 m, y = 0.0 m. (k = 1/4πε 0 = N m 2 /C 2 ) A) 0.56 i^n/c B) i^ N/C C) i^ N/C D) 0.28 i^n/c 1) 2) SHORT ANSWER. Write the word or phrase that best completes each statement or answers the 3) Two thin 80.0-cm rods are oriented at right angles to each other. Each rod has one end at the origin of the coordinates, and one of them extends along the +x-axis while the other extends along the +y-axis. The rod along the +x-axis carries a charge of µc distributed uniformly along its length, and the other rod carries µc uniformly over its length. Find the magnitude and direction of the net electrical force that these two rods exert on an electron located at the point (40.0 cm, 40.0 cm). (e = C, ε 0 = C 2 /N m 2 ) 3) 1

2 MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the 4) The figure shows three electric charges labeled Q 1, Q 2, Q 3, and some electric field lines in the region surrounding the charges. What are the signs of the three charges? 4) A) Q 1 is negative, Q 2 is positive, Q 3 is negative. B) Q 1 is positive, Q 2 is positive, Q 3 is negative. C) Q 1 is positive, Q 2 is negative, Q 3 is positive. D) All three charges are negative. E) All three charges are positive. 2

3 5) An electric dipole consists of charges ±5.00 µc separated by 1.20 mm. It is placed in a vertical electric field of magnitude 525 N/C oriented as shown in the figure. The magnitude of the net torque this field exerts on the dipole is closest to 5) A) N m. B) N m. C) N m. D) N m. E) N m. 6) Two small insulating spheres are attached to silk threads and aligned vertically as shown in the figure. These spheres have equal masses of 40 g, and carry charges q 1 and q 2 of equal magnitude 2.0 µc but opposite sign. The spheres are brought into the positions shown in the figure, with a vertical separation of 15 cm between them. Note that you cannot neglect gravity. (k = 1/4πε 0 = N m 2 /C 2 ) The tension in the lower thread is closest to 6) A) 1.2 N. B) 2.0 N. C) 1.4 N. D) 1.6 N. E) 1.8 N. 3

4 SHORT ANSWER. Write the word or phrase that best completes each statement or answers the 7) In the figure, charge q 1 = C is placed at the origin and charge q 2 = C is placed on the x-axis, at x = m. Where along the x-axis can a third charge Q = -8.3 µc be placed such that the resultant force on this third charge is zero? 7) MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the 8) A point charge Q is located a short distance from a point charge 3Q, and no other charges are present. If the electrical force on Q is F, what is the electrical force on 3Q? A) 3F B) F/3 C) 3F D) F/ 3 E) F 9) The electric field 1.5 cm from a very small charged object points toward the object with a magnitude of 180,000 N/C. What is the charge on the object? (k = 1/4πε 0 = N m 2 /C 2 ) A) +4.5 nc B) +5.0 nc C) -5.0 nc D) -4.5 nc 10) At a distance of 4.3 cm from the center of a very long uniformly charged wire, the electric field has magnitude 2000 N/C and is directed toward the wire. What is the charge on a 1.0 cm length of wire near the center? (ε 0 = C 2 /N m 2 ) A) nc B) nc C) nc D) nc 8) 9) 10) 4

5 11) Two point charges, Q 1 = -1.0 µc and Q 2 = µc, are placed as shown in the figure. (k = 1/4πε 0 = N m 2 /C 2 ) The y component of the electric field, at the origin O, is closest to 11) A) N/C. B) N/C. C) N/C. D) N/C. E) N/C. 12) The figure shows two unequal point charges, q and Q, of opposite sign. Charge Q has greater magnitude than charge q. In which of the regions X, Y, Z will there be a point at which the net electric field due to these two charges is zero? 12) A) only region X B) only region Z C) only region Y D) only regions X and Z E) all three regions 13) An atomic nucleus has a charge of +40e. What is the magnitude of the electric field at a distance of 1.0 m from the center of the nucleus? (k = 1/4πε 0 = N m 2 /C 2, e = C) A) N/C B) N/C C) N/C D) N/C E) N/C 13) 5

6 14) Two point charges Q 1 and Q 2 of equal magnitudes and opposite signs are positioned as shown in the figure. Which of the arrows best represents the net electric field at point P due to these two charges? 14) A) A B) B C) C D) D E) The field is equal to zero at point P. SHORT ANSWER. Write the word or phrase that best completes each statement or answers the 15) Three point charges are placed on the x-axis. A charge of +2.0 µc is placed at the origin, -2.0 µc to the right at x = 50 cm, and +4.0 µc at the 100 cm mark. What are the magnitude and direction of the electrostatic force that acts on the charge at the origin? (k = 1/4πε 0 = N m 2 /C 2 ) 15) 6

7 MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the 16) A point charge Q of mass 8.50 g hangs from the horizontal ceiling by a light 25.0-cm thread. When a horizontal electric field of magnitude 1750 N/C is turned on, the charge hangs away from the vertical as shown in the figure. The magnitude of Q is closest to 16) A) 27.5 µc. B) 3.0 µc. C) 3.5 µc. D) 47.6 µc. E) 55.0 µc. 17) In the figure, a small spherical insulator of mass kg and charge µc is hung by a thin wire of negligible mass. A charge of µc is held m away from the sphere and directly to the right of it, so the wire makes an angle θ with the vertical, as shown. What is the angle θ? (k = 1/4πε 0 = N m 2 /C 2 ) 17) A) 1.30 B) 1.70 C) 1.10 D) E)

8 18) A proton is placed in an electric field of intensity 700 N/C. What are the magnitude and direction of the acceleration of this proton due to this field? (m proton = kg, e = C) A) m/s 2 opposite to the electric field B) m/s 2 opposite to the electric field C) m/s 2 in the direction of the electric field D) m/s 2 in the direction of the electric field E) m/s 2 opposite to the electric field 19) When two point charges are 2.0 cm apart, each one experiences a 1.0-N electric force due to the other charge. If they are moved to a new separation of 8.0 cm, the electric force on each of them is closest to A) 0.25 N. B) 16 N. C) 1.0 N. D) N. E) 4.0 N. 20) When two point charges are a distance d part, the electric force that each one feels from the other has magnitude F. In order to make this force twice as strong, the distance would have to be changed to A) d/ 2. B) 2d. C) d/4. D) 2d. E) d/2. 18) 19) 20) 8