Inner Wire Loop 25. A charged capacitor C, resistor R, and switch S are connected in series. Voltmeter V is connected in parallel with the resistor, as shown in the figure above. At time f = 0, the switch is then closed. Which of the following shows the potential difference A reading on the voltmeter as a 26. Two concentric circular wire loops carry equal function of time t after the switch is closed? currents / in opposite directions, as shown in the figure above. The inner loop has a radius a and (A) AV carries a counterclockwise current. The outer loop has a radius b and carries a clockwise current. What is the magnitude and direction of the magnetic field at the center of the loops? Magnitude Direction AV (B) (A) Hof (1 - - Out of the page (B) of (1 _ 1) Into the page (C) Zero Undefined since magnitude is zero (D) 4 Mol (1 1\\ 2n a b Out of the page Mol(1 _1\\ (E) 21 a b Into the page (D) AV (E)Positively Uniform Magnetic Field Changed -FI $1/2 Particle R 3R O W 29. When a battery is connected to an external resistance R, as shown above on the left, 27. A positively charged particle moves in the there is a current / in the circuit. When the positive x-direction in a uniform magnetic field external resistance is changed to 3R, the directed in the positive y-direction. The net force current changes to 1/2, as shown above on on the particle could be zero if there is also an the right. What is the internal resistance r electric field present in the of the battery? (A) positive z-direction (A) R/4 (B) negative z-direction (C) positive x-direction (B) R/ 2 (D) negative x-direction (C) R E) negative y-direction (D) 2R (E) 4R 30. The advantage of using a dielectric in a capacitor is that it B (A) increases the capacitance of the capacitor (B) increases the conductivity of the capacitor (C) decreases the charging time of the capacitor (D) makes the capacitor dissipate less power E) eliminates the electric field in the capacitor 28. Three identical capacitors with capacitance Care arranged as shown above. What is the equivalent capacitance between points A and B? (A) C/3 (B) 2C/3 (C) C (D) 3C/2 (E) 3C