ART

38) The figure shows four Gaussian surfaces surrounding a distribution of charges. (a) Which Gaussian surfaces have an electric flux of +q/εo through them? (b) Which Gaussian surfaces have no electric flux through them?

Answer: (a) surface b (b) surface c

17) Four point charges of equal magnitudes but with varying signs are arranged on three of the corners and at the center of the square of side d as shown in the figure. Which one of the arrows shown represents the net force acting on the center charge? A) A B) B C) C D) D

Answer: A

20) Four point charges of varying magnitude and sign are arranged on the corners of the square of side d as shown in the figure. Which one of the arrows shown represents the net force acting on the point charge with a charge +Q? A) A B) B C) C D) D

Answer: A

26) The figure shows two unequal charges, +q and -Q. Charge -Q has greater magnitude than charge +q. Point X is midway between the charges. In what section of the line will there be a point where the resultant electric field is zero? A) VW B) WX C) XY D) YZ

Answer: A

29) Three equal-magnitude point charges of varying signs are placed at the corners of a square of side d as shown in the figure. Which one of the arrows shown represents the direction of the net electric field at the center of the square? A) A B) B C) C D) D

Answer: A

37) Which one of the arrows shown in the figure best represents the direction of the electric field between the two uniformly charged metal plates? A) A B) B C) C D) D E) None of the above

Answer: A

12) A hydrogen nucleus, which has a charge +e, is situated to the left of a carbon nucleus, which has a charge +6e. Which statement is true? A) The electrical force experienced by the hydrogen nucleus is to the left, and the magnitude is equal to the force exerted on the carbon nucleus. B) The electrical force experienced by the hydrogen nucleus is to the left, and the magnitude is greater than the force exerted on the carbon nucleus. C) The electrical force experienced by the hydrogen nucleus is to the left, and the magnitude is less than the force exerted on the carbon nucleus. D) The electrical force experienced by the hydrogen nucleus is to the right, and the magnitude is equal to the force exerted on the carbon nucleus.

Answer: A

18) Four point charges of equal magnitude but with varying signs are arranged on three of the corners and at the center of the square of side d as shown in the figure. Which one of the arrows shown represents the net force acting on the center charge? A) A B) B C) C D) D

Answer: A

28) Three equal positive point charges +q are placed at the corners of a square of side d as shown in the figure. Which one of the arrows shown represents the direction of the net electric field at the center of the square? A) A B) B C) C D) D

Answer: A

3) A plastic rod is charged up by rubbing a wool cloth and brought to an initially neutral metallic sphere that is insulated from ground. It is allowed to touch the sphere for a few seconds, and then is separated from the sphere by a small distance. After the rod is separated the rod A) is repelled by the sphere. B) is attracted to the sphere. C) feels no force due to the sphere.

Answer: A

36) A solid aluminum cube rests on a wooden table in a region where a uniform external electric field is directed straight upward. What can we say concerning the charge on the top surface of the cube? A) The top surface is charged positively. B) The top surface is charged negatively. C) The top surface is neutral. D) The top surface's charge cannot be determined without further information.

Answer: A

7) A negatively-charged rod is brought close to (but does not touch) two neutral spheres that are in contact with each other but insulated from the ground. If the two spheres are then separated, what kind of charge will be on the spheres? A) The sphere near the charged rod becomes positive and the other one becomes negative. B) The sphere near the charged rod becomes negative and the other one becomes positive. C) The spheres do not get any charge. D) Both spheres become negative. E) Both spheres become positive.

Answer: A

35) A conductor is placed in a steady external electric field. Which of the following statements are correct for this situation? (There could be more than one correct choice.) A) The electric field is zero inside the conductor. B) All the free electrons go to the surface of the conductor. C) The surface of the conductor is neutral. D) The electric field just outside the surface of the conductor is perpendicular to the surface. E) None of the above statements are correct.

Answer: A, B, D

11) A small charged plastic ball is vertically above another charged small ball in a frictionless test tube as shown in the figure. The balls are in equilibrium a distance d apart. If the charge on each ball is doubled, the equilibrium distance between the balls in the test tube would become A) d. B) 2d. C) 4d. D) 8d. E) d/4.

Answer: B

31) Three equal negative point charges -q are placed at three of the corners of a square of side d as shown in the figure. Which one of the arrows shown represents the direction of the net electric field at the vacant corner of the square? A) A B) B C) C D) D

Answer: B

32) Three equal-magnitude point charges of varying signs are placed at three of the corners of a square of side d as shown in the figure. Which one of the arrows shown represents the direction of the net electric field at the vacant corner of the square? A) A B) B C) C D) D

Answer: B

16) Three equal charges +Q are at three of the corners of a square of side d. A fourth charge +Q of equal magnitude is at the center of the square as shown in the figure Which one of the arrows shown represents the net force acting on the charge at the center of the square? A) A B) B C) C D) D

Answer: B

21) An electron and a proton are released simultaneously from rest and start moving toward each other due to their electrostatic attraction, with no other forces present. Which of the following statements are true just before they are about to collide? (There could be more than one correct choice.) A) They are closer to the to the initial position of the electron that to the initial position of the proton. B) They are closer to the to the initial position of the proton that to the initial position of the electron. C) They are at the midpoint of their initial separation. D) They both have the same speed. E) The electrostatic force on the proton is greater than the electrostatic force on the electron.

Answer: B

27) The electric field at point P due to a point charge Q a distance R away from P has magnitude E. In order to double the magnitude of the field at P, you could A) double the distance to 2R. B) double the charge to 2Q. C) reduce the distance to R/2. D) reduce the distance to R/4. E) double the charge to 2Q and at the same time reduce the distance to R/2.

Answer: B

4) A negatively-charged plastic rod is brought close to (but does not touch) a neutral metal sphere that is connected to ground. After waiting a few seconds the ground connection is removed (without touching the sphere), and after that the rod is also removed. The sphere is now A) negatively charged. B) positively charged. C) neutral.

Answer: B

6) Two uncharged metal spheres, #1 and #2, are mounted on insulating support rods. A third metal sphere, carrying a positive charge, is then placed near #2. Now a copper wire is momentarily connected between #1 and #2 and then removed. Finally, sphere #3 is removed. In this final state A) spheres #1 and #2 are still uncharged. B) sphere #1 carries positive charge and #2 carries negative charge. C) sphere #1 carries negative charge and #2 carries positive charge. D) spheres #1 and #2 both carry positive charge. E) spheres #1 and #2 both carry negative charge.

Answer: B

8) Two tiny beads are 25 cm apart with no other charges or fields present. Bead A carries 10 µC of charge and bead B carries 1 µC. Which one of the following statements is true about the magnitudes of the electric forces on these beads? A) The force on A is 10 times the force on B. B) The force on B is 10 times the force on A. C) The force on A is exactly equal to the force on B. D) The force on A is 100 times the force on B. E) The force on B is 100 times the force on A.

Answer: C

13) Two identical small charged spheres are a certain distance apart, and each one initially experiences an electrostatic force of magnitude F due to the other. With time, charge gradually diminishes on both spheres by leaking off. When each of the spheres has lost half its initial charge, what will be the magnitude of the electrostatic force on each one? A) 1/16 F B) 1/8 F C) 1/4 F D) 1/2 F E) 1/ F

Answer: C

25) Four tiny charged particles (two having a charge +Q and two having a charge -Q) are distributed on the x- and y-axes as shown in the figure. Each charge is equidistant from the origin. In which direction is the net electric field at the point P on the y-axis? A) directly up (in the +y direction) B) directly left (-x direction) C) upwards and towards the left D) upwards and towards the right E) The net field is zero, so there is no direction.

Answer: C

30) Three equal negative point charges -q are placed at three of the corners of a square of side d as shown in the figure. Which one of the arrows shown represents the direction of the net electric field at the center of the square? A) A B) B C) C D) D

Answer: C

39) Gaussian surfaces A and B enclose the same positive charge +Q. The area of Gaussian surface A is three times larger than that of Gaussian surface B. The electric flux through Gaussian surface A is A) nine times larger than the flux of electric field through Gaussian surface B. B) three times larger than the flux of electric field through Gaussian surface B. C) equal to the flux of electric field through Gaussian surface B. D) three times smaller than the flux of electric field through Gaussian surface B. E) unrelated to the flux of electric field through Gaussian surface B.

Answer: C

9) Two very small plastic balls of equal mass are released from rest. One of them carries +10 µC of excess charge and the other one carries +1µC of charge. No other charges or fields are present. Which of the following statements are true about them as they move away from each other? (There may be more than one correct choice.) A) The acceleration of the 10-µC ball is 10 times that of the 1-µC ball. B) The acceleration of the 1-µC ball is 10 times that of the 10-µC ball. C) The balls always have accelerations of equal magnitude. D) The speed of the balls keeps increasing. E) The acceleration of the balls keeps increasing.

Answer: C, D

19) Four point charges Q of equal magnitude and sign are arranged on three of the corners of the square of side d as shown in the figure Which one of the arrows shown represents the net force acting on the charge at the upper right hand corner of the square? A) A B) B C) C D) D

Answer: D

24) An electron is initially moving to the right when it enters a uniform electric field directed upwards, as shown in the figure. Which trajectory (X, Y, Z, or W) will the electron follow in the field? A) trajectory W B) trajectory X C) trajectory Y D) trajectory Z

Answer: D

5) X and Y are two initially uncharged metal spheres on insulating stands, and they are in contact with each other. A positively charged rod R is brought close to X as shown in part (a) of the figure. Sphere Y is now moved away from X, as shown in part (b). What are the final charge states of X and Y? A) Both X and Y are neutral. B) X is positive and Y is neutral. C) X is neutral and Y is positive. D) X is negative and Y is positive. E) Both X and Y are negative.

Answer: D

2) If two objects are electrically attracted to each other A) both objects must be negatively charged. B) both objects must be positively charged. C) one object must be negatively charged and the other object must be positively charged. D) the objects could be electrically neutral. E) None of the above statements are absolutely true.

Answer: D

34) Two stationary point charges q1 and q2 are shown in the figure along with a sketch of some field lines representing the electric field produced by them. What can you deduce from the sketch? A) q1 is negative and q2 is positive; the magnitudes are equal. B) q1 and q2 have the same sign; the magnitudes are equal. C) q1 is positive and q2 is negative; the magnitude of q1 is greater than the magnitude of q2. D) q1 is negative and q2 is positive; the magnitude of q1 is less than the magnitude of q2. E) q1 and q2 have the same sign; the magnitude of q1 is greater than the magnitude of q2.

Answer: D

10) In outer space, a positive charge q is released near a positive fixed charge Q, as shown in the figure. As q moves away from Q, what is true about the motion of q? (There may be more than one correct choice.) A) It will move with decreasing speed. B) It will move with constant acceleration. C) It will move with increasing acceleration. D) It will move with decreasing acceleration. E) It will move with increasing speed.

Answer: D, E

14) Two point charges, Q1 and Q2, are separated by a distance R. If the magnitudes of both charges are doubled and their separation is also doubled, what happens to the electrical force that each charge exerts on the other one? A) It increases by a factor of 2. B) It increases by a factor of . C) It is reduced by a factor of . D) It increases by a factor of 4. E) It remains the same.

Answer: E

15) Two point charges, Q1 and Q2, are separated by a distance R. If the magnitudes of both charges are halved and their separation is also halved, what happens to the electrical force that each charge exerts on the other one? A) It increases by a factor of 16. B) It increases by a factor of 8. C) It increases by a factor of 2. D) It increases by a factor of 4. E) It remains the same.

Answer: E

1) Electrically neutral objects cannot exert an electrical force on each other but they can exert a gravitational force on each other. A) True B) False,

B