Physics 202 MWF 10:20 Spring 2000 (Ford)

Exam II Chapts. 20--22 in Cutnell and Johnson 4e

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

(3 pts) 1. Two capacitors are connected in series as shown in the sketch. After the charges on the capacitors have reached their final values, the voltage on capacitor C₁ is V₁ = 20 V. What is the voltage V₂ on C₂?

a) 5 V
b) 10 V <-------- answer
c) 20 V
d) 40 V
e) 80 V


(3 pts) 2. Two identical resistors are connected to a battery of negligible internal resistance. Will more total power be dissipated by the two resistors if they are connected in series, in parallel, or is the power the same?

a) series
b) parallel <-------- answer
c) same for series as for parallel


(3 pts) 3. A circular wire loop carries current I and is in a region of uniform magnetic field. In which case is the magnitude of the torque exerted on the particle by the magnetic field the greatest:

a) when the magnetic field is parallel to the plane of the loop? <-------- answer
b) when the magnetic field is perpendicular to the plane of the loop?


(3 pts) 4. A charged particle enters a region of magnetic field at point a and travels along the path shown, exiting the field region at point b. The magnetic field in the region is uniform and directed into the plane of the figure. Is the sign of the charge positive or negative?

a) positve
b) negative <-------- answer


Show all your work. Partial credit will be given if earned. Write your answers in the blanks provided.


(10 pts) 5. A coil has 400 turns. The current in the coil is 0.200 A and the average magnetic flux through each turn of the coil is 5.0 × 10^-6 Wb.

a) What is the self-inductance of the coil?

Ans. ____0.01 H_____

b) If the current in this same coil is changing at the rate of 3.0 A/s, what is the magnitude of the emf induced in the coil?

Ans. ____0.03 V___


(21 pts) 6. Consider the circuit shown in the sketch. Calculate the current in each resistor.

Ans. I₁ = ____8 A_____

I₂ = _____4 A____

I₃ = ____6 A____

I₄ = ____6 A____


(21 pts) 7. Consider the circuit shown in the sketch. Note that two currents are given.

a) What is the magnitude of the current I₃ in R₃?

Ans. ____2 A____


b) What are the emfs ₁ and ₂?

Ans. ₁ = ____40 V____

₂ = ___50 V____

c) What is the potential difference V_ab between points a and b? Which point, a or b is at higher potential?

V_ab = ____- 25 V____

point at higher potential is point ___b____


(18 pts) 8. An electron (charge q =-e = -1.6 × 10^-19 C) is moving in the vicinity of a long, straight wire that carries a current I = 5.0 A in the direction shown in the sketch. At a particular instant the electron is 0.080 m above the wire and it is traveling at a speed of v = 6.0 × 10³ m/s in a direction perpendicular to the wire and away from it.

a) What are the magnitude and direction of the magnetic field produced by the current in the wire at the location of the electron? (Specify the direction as to the left, to the right, toward the top of the page, toward the bottom of the page, into the page, out of the page.)

Ans. B = _____1.25 × 10^-5 T_______

direction ____out of page_____

b) What are the magnitude and direction of the force that the magnetic field of the current exerts on the electron? (Specify the direction as to the left, to the right, toward the top of the page, toward the bottom of the page, into the page, out of the page.)

Ans. F = ___1.2 × 10^-20 N________________

direction ___to the left____


(18 pts) 9. In the sketch below the rod ab makes contact with metal rails that are 0.50 m apart. The resistance of the rail plus rod circuit is 5.0 and may be considered to be constant. There is a uniform magnetic field with magnitude B = 2.0 T and direction out of the plane of the paper. The rod is pulled to the left at a constant speed of v = 0.40 m/s.

a) Is the induced current in the circuit clockwise or counterclockwise? (Show the direction of the induced current on the sketch.)

Ans. ____clockwise____

b) What is the magnitude of the induced current?

Ans. ____0.08 A____

c) What external force F_ext is required to move the rod at this constant speed?

Ans. ____0.08 N____