Physics 202 MWF 10:20 Spring 2002 (Ford)

Exam II Chapts. 20--22 in Cutnell and Johnson 5e

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

(3 pts) 1. Consider the circuit shown in sketch (a). The resistor R₂ is removed, to produce the circuit shown in (b). What happens to the current in R₁ when R₂ is removed from the circuit?



(a) stays the same
(b) increases
(c) decreases


(3 pts) 2. Consider the circuit shown in the sketch (a). A resistor R₃ is added, in parallel with R₂. When R₃ is added, what happens to the current through R₁?



(a) stays the same
(b) increases
(c) decreases


(3 pts) 3. An electron is moving in the vicinity of a long, straight wire. If the electron velocity and current directions are as shown, what is the direction of the force exerted by the wire on the electron?



(a) up
(b) down
(c) left
(d) right
(e) into page
(f) out of page


(3 pts) 4. A wire loop is being pushed into a region of uniform magnetic field, as shown in the sketch. As the loop is being pushed in, the induced current is



(a) clockwise
(b) counterclockwise
(c) zero


(3 pts) 5. A wire loop is in a region of uniform magnetic field that is directed into the page, away from you. If the magnetic field is increasing, the induced current is



(a) zero
(b) clockwise
(c) counterclockwise


(3 pts) 6. A conducting rod is being pulled to the left through a region of uniform magnetic field that is directed into the page. Which statement about the potential V_a at point a and potential V_b at point b is correct?



(a) V_a > V_b
(b) V_a < V_b
(c) V_a = V_b


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


(20 pts) 7. Consider the circuit shown in the sketch. Note that one current is given.



a) What is the current through the 6 resistor?

Ans. ________________

b) What is the current through the 2 resistor?

Ans. ________________

c) What is the voltage V of the battery in the bottom branch of the circuit?

Ans. _______________

d) What is the potential difference between points a and b and which point is at higher potential?

Ans. _________________


(20 pts) 8. Three capacitors C₁ = 5 µF, C₂ = 3 µF, and C₃ = 6 µF are connected to a battery as shown in the sketch. After the charges on the capacitors have reached their final values, the charge on C₂ is 4.0 × 10^-5 C.



a) What is the charge on capacitor C₃?

Ans. ____________________

b) What is the charge on capacitor C₁

Ans. ___________________

c) What is the voltage V of the battery?

Ans. _________________


(21 pts) 9. The triangular loop of wire shown in the sketch carries a current of I = 5 A in the direction shown. Find the force exerted by the magnetic field on each side of the triangle. If the force is not zero, specify its direction. The magnetic field is uniform, has magnitude B = 3 T, and is in the direction shown.



a) side PQ

Ans. ________________

direction? ________________

b) side QR

Ans.___________________

direction? ____________

c) side PR

Ans._______________

direction?____________

d) The area of the loop is 0.24 m². If the loop is pivoted about an axis that lies along side PR, what is the magnitude of the torque exerted by the magnetic field on the loop?

Ans. _____________________


(21 pts) 10. A conducting rod of length 1.5 m moves to the right at constant speed along conducting rails. There is a uniform magnetic field of B = 3.0 T that is directed into the plane of the figure. An electric heater with resistance 8.0 is connected between the rails, the induced current passes through the heater, and the heater consumes 24 W of power.



a) How fast is the bar moving?

Ans. ___________________

b) Is the current in the circuit clockwise or counterclockwise?

Ans. _____________________

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

Ans. _____________