Download Midterm Exam #3 - General Physics | PHYS 115 and more Exams Physics in PDF only on Docsity!
Name: _____________________________________________Student ID # ______________________ Last First
Physics 115A Fall- 2010 November 30 , 2010
Practice Midterm Exam 3
PART ONE , Multiple choice
Use scantron and pencil. Mark your answers on the exam for reference. Make sure that All pages have your name and student ID on them!!! Five points for each correct answer in the multiple choice section.
1. Two light bulbs are designed for use with the same voltage. The ratio of the resistance of the two bulbs is 2:1. If the dimmer bulb is of 60 W, what is the power of the brighter light bulb?
A) 30 W B) 60 W C) 120 W D) 360 W E) 240 W
Use the following to answer question 2:
Three resistors are connected as shown in the figure. The current in the 3- resistor is 6 A.
2. What is the potential difference between the points^ A^ and^ B?
A) 28 V B) 32 V C) 26 V D) 38 V E) 42 V
3. A portion of a circuit is shown, with the values of the currents given for some branches. What is the direction and value of the current I?
A) , 6A B) , 6A C) , 4A D) , 4A E) , 8A
Last First
4. Three parallel plate capacitors, each having a capacitance of 1.0 μF are connected in parallel. The potential difference across the combination is 100 V. What is the charge on any one of the capacitors?
A) 30 C B) 100 C C) 300 C D) 1000 C E) 3000 C
5. An electron traveling due north enters a region that contains a uniform magnetic field that points due east. In which direction will the electron be deflected?
A) east B) west C) down D) up E) south
Use the following to answer question 6:
An RC circuit consists of a resistor with resistance 1.0 k, a 120-V battery, and two capacitors, C 1 and C 2 , with capacitances of 20 μF and 60 μF, respectively. Initially, the capacitors are uncharged; and the switch is closed at t = 0 s.
6. Determine the total charge on both capacitors two time constants after the switch is closed.
A) 1.3 10 ^3 C B) 2.2 10 ^3 C C) 4.7 10 ^3 C D) 6.1 10 ^3 C E) 8.3 10 ^3 C
7. A 0.150-m wire oriented horizontally between the poles of an electromagnet carries a direct current of 12.5 A. The angle between the direction of the current and that of the magnetic field is 25.0°. If the magnetic field strength is 0.625 T, what is the magnitude and direction of the magnetic force on the wire between the poles?
A) 1.17 N, upward D) 1.44 N, downward B) 3.30 N, downward E) 0.495 N, upward C) 0.792 N, upward
Last First Physics 115A Fall- 2010 November 30 , 2010
Practice Midterm Exam 3
PART TWO , Handwritten problems
Answer all questions as completely as possible in the blank spaces below. Specify the units used. Continue on the back side if necessary. Show your work. Give all reasoning, equations, and calculations. Partial credit will be given for incomplete answers.
- Two batteries and three resistors are connected as shown below. (a) Find the current through each battery when the switch is closed. (b) Is the potential at point A greater than, less than, or equal to the potential at point B?
A. Take the current, I 1 , to flow clockwise from positive terminal of the 6.0-V battery, the current, I 2 , to flow clockwise from positive terminal of the 9.0-V battery, and the current, I 3 , to flow clockwise through the 5-Ω resistor. Applying the junction rule at A gives: 2 pt
B. Apply the loop rule to the left side of the circuit, traversing it in the clockwise direction. The respective equation is: 4 pts
C. Apply the loop rule around the outside of the circuit, traversing it in the clockwise direction. The respective equation is: 4 pts
D. Solve the system of equations in (A), (B), and (C) for I , I 1 and I 2. The numeric values are: 8 pts
E. Is the potential at point A greater than, less than, or equal to the potential at point B? Encircle your answer. Explain your choice. 2 pts (1) Greater than at B (2) less than at B (3) Equal to that at B
F. Explain your choice: 5 pts
Last First
- The figure below shows a zero-resistance massless rod moving to the right on two frictionless zero- resistance rails separated by the distance L = 0.45 m. The rails are connected by a 12.5- Ω resistor and the entire system is in a uniform magnetic field with a magnitude of 0.750 T. (a) Find the speed at which the rod must be moved to produce a current of 0.125 A. (b) Find the force that must be exerted on the rod to maintain this constant current in the resistor. (c) What is the rate of energy dissipation in the resistor?
A. Find the motional emf in the loop providing the current of 0.125 A in the resistor. 3 pts
B. Express the emf in the loop in terms of the rate of change of the area encountered by the loop. 5 pts
C. Evaluate the rate of change of the area encountered by the loop. 4 pts
D. Find the velocity v of the rod determining this rate of change of area. 5 pts
E. Find the magnetic force on the moving rod with the current I = 0.125 A in the loop. 3 pts
F. What is the rate of energy dissipation in the resistor? 5 pts
