PRACTICE EXAM 1 for Midterm 2

Multiple Choice Questions 1) The figure shows three identical lightbulbs connected to a battery having a constant voltage across its terminals. What happens to the brightness of lightbulb 1 when the switch S is closed? A) The brightness will increase momentarily then return to its previous level. B) The brightness increases permanently. C) The brightness will decrease momentarily then return to its previous level. D) The brightness remains the same as before the switch is closed. E) The brightness decreases permanently. Answer: B 2) A resistor and a capacitor are connected in series across an ideal battery having a constant voltage across its terminals. At the moment contact is made with the battery (a) the voltage across the capacitor is A) equal to the battery's terminal voltage. B) less than the battery's terminal voltage, but greater than zero. C) equal to the battery's terminal voltage. D) zero. (b) the voltage across the resistor is A) equal to the battery's terminal voltage. B) less than the battery's terminal voltage, but greater than zero. C) equal to the battery's terminal voltage. D) zero. Answer: (a) D (b) C

3) Three particles travel through a region of space where the magnetic field is out of the page, as shown in the figure. The electric charge of each of the three particles is, respectively, A) 1 is neutral, 2 is negative, and 3 is positive. B) 1 is neutral, 2 is positive, and 3 is negative. C) 1 is positive, 2 is neutral, and 3 is negative. D) 1 is positive, 2 is negative, and 3 is neutral. E) 1 is negative, 2 is neutral, and 3 is positive. Answer: E 4) Ions having equal charges but masses of M and 2M are accelerated through the same potential difference and then enter a uniform magnetic field perpendicular to their path. If the heavier ions follow a circular arc of radius R, what is the radius of the arc followed by the lighter? A) 4R B) 3R C) 2 R D) R/ 2 E) R/2 Answer: D

5) The figure shows four different sets of insulated wires that cross each other at right angles without actually making electrical contact. The magnitude of the current is the same in all the wires, and the directions of current flow are as indicated. For which (if any) configuration will the magnetic field at the center of the square formed by the wires be equal to zero? A) A B) B C) C D) D E) The field is not equal to zero in any of these cases. Answer: C 6) Consider a solenoid of length L, N windings, and radius b (L is much longer than b). A current I is flowing through the wire. If the radius of the solenoid were doubled (becoming 2b), and all other quantities remained the same, the magnetic field inside the solenoid would A) remain the same. B) become twice as strong. C) become one half as strong. Answer: A 7) In the figure, two solenoids are approaching each other with speed v as shown. The induced current through the resistor R is A) from a to b. B) from b to a. C) There is no induced current through the resistor. Answer: A

8) A circular loop of wire lies in the plane of the paper. An increasing magnetic field points out of the paper. What is the direction of the induced current in the loop? A) counter-clockwise then clockwise B) clockwise then counter-clockwise C) clockwise D) counter-clockwise E) There is no current induced in the loop. Answer: C 9) Which of the following statements about inductors are correct? There may be more than one correct choice. A) When it is connected in a circuit, an inductor always resists having current flow through it. B) Inductors store energy by building up charge. C) When an inductor and a resistor are connected in series with a DC battery, the current in the circuit is reduced to zero in one time constant. D) An inductor always resists any change in the current through it. E) When an inductor and a resistor are connected in series with a DC battery, the current in the circuit is zero after a very long time. Answer: D 10) An insulated wire of diameter 1.0 mm and negligible resistance is wrapped tightly around a cylindrical core of radius 5.0 cm and length 30 cm to build a solenoid. What is the energy stored in this solenoid when a current I = 0.20 A flows through it? (μ0 = 4π 10-7 T m/a) A) 1.2 10-4 J B) 9.6 10-4 J C) 4.8 10-4 J D) 2.4 10-4 J E) 5.9 10-5 J Answer: E