# Physics Electrodynamics

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• Published : April 16, 2013

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| 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 | | |
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| 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| | |
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| 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 | | |
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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| | |
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| The work required to move a charge, q = e from infinity to r = 2 m is| A)| 4000 eV| D)| 4000 eV|
B)| 2000 eV| E)| zero|
C)| 1000 eV| | |
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| A 2.0-µF capacitor has a potential difference of 5000 V. The work done in charging it was | | A) 2.5 J B) 5.0 J C) 25 J D) 5.0 mJ E) 0.50 kJ | | |
| A coaxial cable consists of a wire of radius 1.0 mm and an outer conducting shell of radius 8 mm. A 20 V potential difference is applied between the wire and the shell. What is the energy stored in a 2 m length of the cable? | | A) 5.35 nJ B) 10.7 nJ C) 2.67 nJ D) 61.6 pJ E) 123 pJ| | |

| Which of the following relations among the quantities in the figure is generally correct? | A)| I1R1 = I2R2 | D)| I3R4 = I4R3 |
B)| I3R3 = I4R4 | E)| I1R1 + I2R2 =  |
C)| I1R1 = I4R4 | | |
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| What is the current through the circuit in the figure? | | A) +0.83 A B) –0.50 A C) +0.50 A D) +0.55 A E) –0.92 A | | |
| An electric motor drives a pump that lifts water from a well that is 11.9 m deep and then delivers the water through a hose at a rate of 180 L/min and a speed of 21.0 m/s. If we assume 100% efficiency and ignore viscosity, the current drawn by the motor from a 220-V source is | | A) 4.6 A B) 7.2 A C) 6.0 A D) 1.0  103 A E) 2.3 A | | |

| An electron (q = 1.6  10–19 C) is traveling east with an instantaneous velocity of 2.5  105 m/s when it enters a uniform magnetic field of 0.45 T that points 35º north of east. What are the magnitude and direction of the force on the electron? | A)| 1.8  10–14 N up | D)| 1.0  10–14 N down | B)| 1.5  10–14 N down | E)| 1.0  10–14 N up | C)| 1.5  10–14 N up | | |

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| The left diagram shows a force F on a negatively charged particle moving a magnetic field B. Using the right diagram, the direction of the velocity of the particle is...