Physics 202 MWF 10:20 Spring 2004 (Ford)

Exam II Chapts. 20--22 in Cutnell and Johnson 6e

Multiple choice questions. Circle the correct answer. No work needs to be shown and no partial credit will be given.

(4 pts) 1. The current in a solenoid is increasing at a constant rate of 0.20 A/s. At the instant when the current in the solenoid is 4.0 A, the emf induced in the solenoid is 0.080 V. What is the inductance L of the solenoid?

(a) 0.020 H
(b) 0.050 H
(c) 0.40 H<--------
(d) 20.0 H


(4pts) 2. A square conducting loop is pivoted about an axis along one edge of the loop, as shown. The loop has a single turn and has area 0.16 m². There is a clockwise current I = 3.0 A in the loop. A uniform magnetic field B = 5.0 T is directed into the page, as shown. The magnitude of the torque exerted on the coil by the magnetic field is



(a) zero<--------
(b) 0.48 N·m
(c) 0.80 N·m
(d) 2.4 N·m
(e) 15.0 N·m


(4 pts) 3. A long, straight wire lies on a table and carries a current I that is to the left, as shown. A small circular conducting loop is pushed across the table away from the wire. When the loop is in the position shown, what is true about the induced current in the loop:



(a) it is clockwise<--------
(b) it is counterclockwise
(c) it is zero


(4 pts) 4. In circuit A two identical resistors are connected in series to an emf source. In circuit B the same two resistors are connected in parallel to the same emf source. In which circuit is the total electrical power delivered by the emf source the greatest?



(a) circuit A
(b) circuit B<--------
(c) the total powered delivered by the source is the same in the two circuits


Show all your work for partial credit. Write your answers in the blanks provided.


(20 pts) 5. The circuit shown in the sketch has a network of three capacitors connected to a battery. After the capacitors have reached their final charges, what is the voltage across the 4.0 µF capacitor?



Ans. ____12 V___


(22 pts) 6. Consider the circuit shown in the sketch. There is a current of 2.0 A flowing to the left through the 5.0 resistor. What are



a) the magnitude of the current in the 8.0 resistor?

Ans. ____3 A_____

b) the emf of the battery that is to the left of the 8.0- resistor?

Ans.____74 V____


(20 pts) 7. Two long, straight parallel wires carry currents in the same directions, as shown. A negative point charge with q = -8.0 ·C moves in the space between the wires. At the instant that the charge is midway between the wires and is moving toward the lower wire, what are the magnitude and direction of the net force exerted by the wires on the charge? (Give the direction of the force as either left, right, toward top of page, toward bottom of page, into page or out of page.)



Ans. magnitude ____1.6 × 10 ^-6 N____

direction ___to the left_____


(22 pts) 8. A bar 0.80 m long moves to the left at speed v on conducting rails. The circuit is completed by a 5.0 resistor connected between the left-hand ends of the rails. There is a uniform magnetic field B =0.40 T directed into the page. At the instant shown, the resistor is consuming electrical energy at a rate of 45.0 W.



a) Is the induced current in the circuit clockwise or is it counterclockwise?

Ans. _____clockwise____

b) What is the speed v of the bar at the instant shown?

Ans. ____46.9 m/s____

(c) What is the magnitude of the external force that must be applied to the bar to keep it moving to the left at the constant speed found in part (b)?

Ans. _____0.96 N_____