TALLER DE ELECTROSTÁTICA

Transcription

1 TALLER DE ELECTROSTÁTICA MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 1) If two objects are electrically attracted to each other, 1) A) the objects could be electrically neutral. B) both objects must be positively charged. C) both objects must be negatively charged. D) one object must be negatively charged and the other object must be positively charged. E) None of the above statements are absolutely true. 2) 2) 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) Both X and Y are negative. D) X is negative and Y is positive. E) X is neutral and Y is positive. 3) 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 B is 100 times the force on A. B) The force on A is 10 times the force on B. C) The force on A is exactly equal to the force on B. D) The force on B is 10 times the force on A. E) The force on A is 100 times the force on B. 4) 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.) 3) 4) A) It will move with increasing acceleration. B) It will move with decreasing speed. C) It will move with decreasing acceleration. D) It will move with increasing speed. E) It will move with constant acceleration. 1

2 5) 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 5) A) d/4. B) 8d. C) 2d. D) 4d. E) 2d. 6) 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) 1/2 F B) 1/16 F C) 1/8 F D) 1/4 F E) 1/ 2 F 6) 7) 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? 7) A) A B) B C) C D) D

3 8) 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? 8) A) A B) B C) C D) D SHORT ANSWER. Write the word or phrase that best completes each statement or answers the question. 9) Two equal and opposite charges are a small distance apart, forming an electric dipole. A positive charge +q is placed above these charges, as shown in the figure, equidistant from both of them. Which diagram below best gives the direction of the net force the dipole exerts on the charge +q? 9)

4 MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 10) 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? 10) A) trajectory W B) trajectory X C) trajectory Y D) trajectory Z 11) 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? 11) A) VW B) WX C) XY D) YZ 12) The figure shows electric field lines arising from two small charged particles P and Q. Consider the following two statements: (i) The charge on P is smaller than the charge on Q. (ii) The electrostatic force on P is smaller than the force on Q. Which of the above statements are true? 12) A) Only (i) is true. B) Only (ii) is true. C) Both (i) and (ii) are true. D) Neither (i) nor (ii) is true.

5 13) Which one of the arrows shown in the figure best represents the direction of the electric field between the two uniformly charged metal plates? 13) A) A B) B C) C D) D E) None of the above 14) How many electrons are necessary to produce 1.0 C of negative charge? (e = C) 14) A) B) C) D) E) ) If a charge generator builds a negative static charge of µc, how many electrons are transferred to it during this process. (e = C) A) 7.0 B) 43.8 C) D) ) An asteroid of mass 58,000 kg carrying a negative charge of 15 µc is 180 m from a second asteroid of mass 52,000 kg carrying a negative charge of 11 µc. What is the magnitude of the net force the asteroids exert upon each other, assuming we can treat them as point particles? (G = N m2/kg2, k = 1/4 0 = N m2/c2) A) N B) N C) 510,000 N D) 570,000 N 17) Two tiny particles having charges of µc and µc are placed along the y-axis. The µC particle is at y = 0.00 cm, and the other particle is at y = cm. Where must a third charged particle be placed along the y-axis so that it does not experience any net electric force due to the other two particles? A) 2.99 m B) m C) m D) m E) m 15) 16) 17)

6 18) One point charge +Q is placed at the center of a square, and a second point charge -Q is placed at the upper-left corner of the square. It is observed that an electrostatic force of magnitude 2.0 N acts on the positive charge at the center. Now a third charge -Q is placed at the lower-left corner of the square, as shown in the figure. What is the magnitude of the net force that acts on the center charge now? 18) A) 4.0 N B) 0.0 N C) 5.3 N D) 2.8 N 19) As shown in the figure, three charges are at the vertices of an equilateral triangle. The charge Q is 6.7 nc, and all the other quantities are accurate to two significant figures. What is the magnitude of the net electric force on the charge Q due to the other two charges? (k = 1/4 0 = N m2/c2) 19) A) N B) N C) N D) N 20) An electron is projected with an initial velocity v0 = m/s along the y-axis, which is the centerline between a pair of charged plates, as shown in the figure. The plates are 1.0 m long and are separated by 0.10 m. A uniform electric field of magnitude E in the +x-direction is present between the plates. If the magnitude of the acceleration of the electron is measured to be m/s2, what is the magnitude of the electric field between the plates? (e = C, melectron = kg) 20) A) 51,000 N/C B) 40,000 N/C C) 35,000 N/C D) 29,000 N/C E) 45,000 N/C