Exam 2 Row: PHY 2140 Seat:
Date, 2003
Please type your name here Please type your student number here
Instructions:
The following procedure must be followed in order to correct any (unlikely) mistakes in the grading.
1. Do all the questions. Show your work for partial credit. I must be able to understand what you have done while I am reading the exam – not when you explain it to me after the exam is graded and returned.
2. For each problem: (a) write down any formula(s) used (b) justify why you used that particular formula(s) (c) copy the answer you have circled from the exam pages to the General Purpose Answer Sheet and fill in the ovals. (d) show your work!
3. The formula sheet is on the last page of the exam. You may detach it from the rest of the exam. NAME
1. What is the current on the 2.00 resistor? 4 12 V
2 a. 1.50 A b. 2.00 A c. 2.50 A d. 3.00 A e. 3.50 A 12 V 4
2. The following five figures show the velocity v of a proton moving in a magnetic field B. Which of the forces F shown in the pictures is impossible? v
a) b) c) v F F v v F
. B B B
F d) e) v B B
F v
3. A 2.0 microcoulomb particle with a kinetic energy of 0.10 J is fired into a uniform magnetic field of magnitude 0.10 T. If the particle moves in a uniform circular path of radius 3.0 m, determine its mass.
a. 1.3 x 10-12 kg b. 1.8 x 10-12 kg c. 3.1 x 10-12 kg d. 3.7 x 10-12 kg e. 4.2 x 10-12 kg NAME
4. At what distance from a long straight wire carrying a current of 5.0 A is the magnetic field due to the wire equal to the strength of the earth’s field, 5.0 x 10-5 T?
a. 0.020 m b. 0.20 m c. 2.0 m d. 20 m e. 200 m
5. A bar of length 0.50 m slides without friction along current carrying rails in a magnetic field of 0.25 T. Find the magnetic force on the bar if the bar carries a 5.00 A current.
a. Zero b. 0.63 N B c. 1.23 N R v d. 1.67 N e. 2.16 N
6. Consider the moving bar from problem 5 and take R = 6.0 . At what speed v must the bar move so that the current is 5.0 A?
a. 40 m/s b. 80 m/s c. 120 m/s d. 240 m/s e. 360 m/s
7. A cube with an edge of length l = 0.04 m is placed in a uniform magnetic field
throughout the region that has components Bx = 0, By = 4 T and Bz = 3 T. Find the flux through the shaded surface. z
a. Zero b. 0.0064 Tm2 c. 0.0048 Tm2 d. 0.12 Tm2 e. 0.16 Tm2 x y NAME
8. Kid Rock presents a golden wedding ring to Pamela Anderson. To impress her, he spins the ring about a vertical axis at a frequency of 60 Hz in a magnetic field of B = 0.5 T as shown. If the area of the ring is 2.0 x 10-4 m2, calculate the maximum emf induced in the ring.
B a. 0.038 V b. 0.046 V c. 0.052 V d. 0.060 V e. Kid Rock was never a member of Tesla, EMF or AC/DC.
9. A bar magnet is positioned next to a solenoid as shown. What is the direction of the current through the resistor when the magnet is moved (1) away from the solenoid and (2) toward the solenoid. v
a. (1) left to right and (2) right to left S N b. (1) right to left and (2) right to left c. (1) left to right and (2) left to right d. (1) right to left and (2) left to right e. lefty losey, righty tighty
10. An emf of 12.0 mV is induced in a 500 turn coil when the current is changing at a rate of 10.0 A/s. What is the magnetic flux through each turn of coil at the instant when the current is 3.00 A?
a. 1.4 x 10-6 Tm2 b. 2.2 x 10-6 Tm2 c. 5.4 x 10-6 Tm2 d. 7.2 x 10-6 Tm2 e. 8.8 x 10-6 Tm2 11. A rectangular loop is placed in a uniform magnetic field with the plane of the loop parallel 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:
a. a net force. b. a net torque. c. a net force and a net torque d. neither a net force nor a net torque.
12. (bonus) The light bulbs in the circuit are identical. When the switch is closed,
a. nothing changes b. both go out. c. the intensity of light bulb A increases. d. the intensity of light bulb A decreases. e. the intensity of light bulb B increases. f. the intensity of light bulb B decreases. g. some combination of 1–5 occurs. 1 v 2 KE mv2 F ma a V IR 2 r 2 1 1 1 2 V P IV P I R Req R1 R2 R Req R1 R2 F qvBsin F BIℓsin Fℓsin NBIAsin mv I NI r B 0 B 0 B A BAcos qB 2r ℓ E N E Bℓv E NAB sint E NAB t max I N N 2 A 2f E L L L 0 t I ℓ 1 PE LI 2 2
2 9 2 2 -19 g = 9.8 m/s ke=8.99 x 10 Nm /C 1 eV = 1.6 x 10 J -12 2 2 6 = 8.85 x 10 C /Nm 1 kWh = 3.60 x 10 J Tm/A