Principles of Chemistry. Chapter 21 Answers

Chapter 21 Sample Multiple Choice Problems 1. A circular loop of radius 0.10 m is rotating in a uniform magnetic field of 0.20 T. Find the magnetic flux through the loop when the plane of the loop and the magnetic field vector are parallel. a. zero b. 3.1X10-3 Tm2 c. 5.5X10-3 Tm2 d. 6.3X10-3 Tm2 2. A circular loop of radius 0.10 m is rotating in a uniform magnetic field of 0.20 T. Find the magnetic flux through the loop when the plane of the loop and the magnetic field vector are perpendicular. a. zero b. 3.1X10-3 Tm2 c. 5.5X10-3 Tm2 d. 6.3X10-3 Tm2 3. A coil is wrapped with 200 turns of wire on a square frame with sides 18 cm. A uniform magnetic field is applied perpendicular to the plane of the coil. If the field changes uniformly from 0.50 T to 0 in 8.0 s, find the average value of the induced emf. a. 2.1 mV b. 4.1 mV c. 0.21 V d. 0.41 V 4. A square coil of wire with 15 turns and an area of 0.40 m2 is placed parallel to a magnetic field of 0.75 T. The coil is flipped so its plane is perpendicular to the magnetic field in 0.050 s. What is the magnitude of the average induced emf? a. 6.0 V b. 36 V c. 45 V d. 90 V 5. The cross-sectional area of an adjustable single loop is reduced from 1.0 m2 to 0.25 m2 in 0.10 s. What is the average emf that is induced in this coil if it is in a region where B = 2.0 T upward, and the coil's plane is perpendicular to B? a. 12 V b. 15 V c. 18 V d. 21 V 6. Doubling the number of loops of wire in a coil produces what kind of change on the induced emf, assuming all other factors remain constant? a. b. c. d. The induced emf is 4 times as much. The induced emf is 3 times as much. The induced emf is twice as much. There is no change in the induced emf. 7. A circular loop of wire is rotated at constant angular speed about an axis whose direction can be varied. In a region where a uniform magnetic field points straight down, what must be the orientation of the loop's axis of rotation if the induced emf is to be zero? a. Any horizontal orientation will do. b. It must make an angle of 45ø to the vertical. c. It must be vertical. d. None of the above. 8. According to Lenz's law, the direction of an induced current in a conductor will be that which tends to produce which of the following effects? a. enhance the effect which produces it. b. produce a greater heating effect. c. produce the greatest voltage. d. oppose the effect which produces it. 9. An transformer consists of a 500-turn primary coil and a 2000-turn secondary coil. If the current in the secondary is 3.0 A, what is the current in the primary? a. 0.75 A b. 1.3 A c. 12 A d. 48 A 10. The potential across an ideal inductor is proportional to a. the current flowing through it. b. the resistance of the circuit. c. the rate of change of current in the coil. d. None of the above. 11. A transformer is a device that a. operates on either DC or AC. b. operates only on AC. c. operates only on DC. d. increases the power level of a circuit. 12. A generator produces 60 A of current at 120 V. The voltage is usualy stepped up to 4500 V by a transformer and transmitted through a power line of total resistance 1.0 Ω. Find the number of turns in the secondary if the primary has 200 turns. a. b. c. d. 13. 5 200 4500 7500 What current flows in a 60-mH inductor when 120 V AC at a frequency of 20 kHz is applied to it? a. 8.0 mA b. 16 mA c. 24 mA d. 32 mA 14. Consider an RLC circuit that is driven by an AC applied voltage. At resonance, a. the peak voltage across the capacitor is greater than the peak voltage across the inductor. b. the peak voltage across the inductor is greater than the peak voltage across the capacitor. c. the current is in phase with the driving voltage. d. the peak voltage across the resistor is equal to the peak voltage across the inductor. 15. What is the current through a 0.0010-æF capacitor at 1000 Hz and 5.0 V? a. 5.4 æA b. 31 æA c. 3.1 mA d. 10 mA Answers: 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. a d d d b c c d c c b d b c b