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Transcript
I-1. Inductor 1 consists of a single loop of wire. Inductor 2 is identical to 1 except it has two loops. How do the selfinductances of the two loops compare? I Coil 2 Coil 1 I A) L2 = 2 L1 B) L2 > 2L1 C) L2 < 2L1 I-2. Two long solenoids, each of inductance L, are connected together to form a single very long solenoid of inductance Ltotal. What is Ltotal? A) 2L + L = B) 4L C) 8L L D) none of these Ltotal = ? I-3. The same current I is flowing through solenoid 1 and solenoid 2. Solenoid 2 is twice as long and has twice as many turns as solenoid 1, and has twice the diameter. (Hint: for a solenoid B = o n I ) I 1 2 I What is the ratio of the magnetic energy contained in U2 solenoid 2 to that in solenoid 1, that is, what is U ? 1 A) 2 B) 4 C) 8 D) 16 E) None of these. I-4. An LR circuit is shown below. Initially the switch is open. At time t=0, the switch is closed. What is the current thru the inductor L immediately after the switch is closed (time = 0+)? R1 = 10 V = 10V A) Zero B) 1 A L = 10H R2 = 10 C) 0.5A D) None of these. After a long time, what is the current from the battery? A) 0A B) 0.5A C) 1.0A D) 2.0A E) None of these. Now suppose the switch has been closed for a long time and is then opened. Immediately after the switch is opened, the current thru R2 is A) zero B) not zero I-5. The switch in the circuit below is closed at t=0. R = 20 V = 10V L = 10H What is the initial rate of change of current dI/dt in the inductor, immediately after the switch is closed ? (Hint:what is the initial voltage across the inductor?) A) 0 A/s B) 0.5A/s C) 1A/s E) None of these. D) 10A/s http://www.youtube.com/watch?v=u5t6PkP1ndc&feature=r elated I-6. A transformer is connected to a battery as shown. The voltage difference across the resistor R is ... A) V N2/N1 B) V N1/N2 C) V D) zero. E) not enough information to answer. V N2 N1 R iron core I-7. The primary coil of a transformer is connected to a battery, a resistor, and a switch. The secondary coil is connected to an ammeter. When the switch is thrown closed, the ammeter shows.. A) a zero current all the time B) a non-zero current for a brief time when the switch is closed C) a steady non-zero current after the switch is closed V A R iron core I-8. A step-down transformer is attached to an AC voltage source and a resistor as shown. How does the current in the resistor I R compare to the current drawn from the AC source Iinput? (With AC circuits, we always use rms values of I and V.) A) I R > I_in B) I R < I_in I_in IR C) I R = I_in D) Depends on the value of Iin I-9. An electrical engineer at a power plant wants to reduce the energy wasted during power transmission from the plant to the city. The power output Po=IV of the plant is fixed at 100MW. The engineer decides to double output voltage V. By what factor does the power lost in the cable (Plost = I2 Rcable) change? Rcable V(AC) I Rcity A) No change B) factor of 2 decrease in power lost C) factor of 4 decrease D) factor of 8 decrease D) Power lost in cable increases A rectangular loop is placed in a uniform magnetic field with the plane of the loop perpendicular to the direction of the field. If a current is made to flow through the loop in the sense shown by the arrows, the field exerts on the loop... B I A) a net force only B) a net torque only C) a net force and a net torque D) neither a net torque nor a net force.