Physics Electrodynamics

| Two small spheres, each with mass m = 3.0 g and charge q, are suspended from a point by threads of length L = 0.22 m. What is the charge on each sphere if the threads make an angle  = 15º with the vertical? | | A) 0.79 C B) 2.9 C C) 75 mC D) 6.3 C E) 0.11 C | | | | Three charges, each of Q = 3.2  10–19 C, are arranged at three of the corners of a 20-nm square as shown. The magnitude of the electric field at D, the fourth corner of the square, is approximately | A) | 1.4  107 N/C | D) | 30 N/C | B) | 1.0  1011 N/C | E) | 1.8  107 N/C | C) | 3.6  1010 N/C | | | | | | An infinitely long cylinder of radius 4.0 cm carries a uniform volume charge density  = 200 nC/m3. What is the electric field at r = 2.0 cm? | | A) zero B) 0.11 kN/C C) 57 N/C D) 0.44 kN/C E) 0.23 kN/C | | A uniform line charge of linear charge density  = 5.00 nC/m extends from x = 0 to x = 10 m. The magnitude of the electric field at x = 12 m is | | A) 3.86 N/C B) 9.62 N/C C) 15.3 N/C D) 18.8 N/C E) 37.5 N/C |

| The electric field in a region is given by where the units are in V/m. What is the potential from the origin to (x, y) = (2, 0) m? | A) | 8 V | D) | –24/3 V | B) | –8 V | E) | 11 V | C) | –16/3 V | | | | | | Two parallel metal plates 5.0 cm apart have a potential difference between them of 75 V. The electric force on a positive charge of 3.2 × 10–19 C at a point midway between the plates is approximately | A) | 4.8 × 10–18 N | D) | 4.8 × 10–16 N | B) | 2.4 × 10–17 N | E) | 9.6 × 10–17 N | C) | 1.6 × 10–18 N | | | | |

Use the following figure to answer the next two problems:The electric field versus distance for a charge is plotted above. Use the reference point V = 0 at r infinity. |

| The potential for r < 1 m is | A) | 4000 V | D) | zero | B) | 2000 V | E) | cannot be determined precisely | C) | 1000 V | |