Midterm2Solution

Midterm2Solution - PHYSICS 9C MIDTERM 2 March 3 , 2011 I...

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PHYSICS 9C MIDTERM 2 March 3 , 2011 I certify by my signature below that I will abide by the UC Davis Code of Academic Conduct. This includes not copying from anyone else’s exam not letting any other student copy from my exam not discussing this exam with any student who has not yet taken it, nor providing any information, written or oral, that might get to a student who has not yet taken it. Anyone suspected of cheating will be automatically reported to Student Judicial Affairs. LAST NAME: FIRST NAME: STUDENT ID: (P R I N T) (P R I N T) (LAST 4 DIGITS) Signature: Problem 1 (two points) . Each resistor here is 1 Ohm. What is the resistance of this bridge? A. 5 Ω B. 1 Ω C. 4/5 Ω D. 1/5 Ω Ε. 0.0 Ω Solution: One sees that if a battery is attached, there will be no current thru central resistor due to complete left/right symmetry. Therefore one can neglect central resistor. Then we have two serially connected resistors from the left and from the right which are then connected in parallel. The resulting resistance is (1/2+1/2)^(-1)=1 Ohm, Answer B

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. B ? . B ? ε 1 ε 2 R 1 R 2 I V A V B + + - - Problem 2. (two points) In the fragment of a circuit shown ε 1 =5 V, ε 2 =10 V, R 1 =3 Ohm, R 2 =5 Ohm and the current is 1 A. What is the potential difference between the points A and B: V A -V B = A. +5 V B. – 3V C. +1 V D. +3 V E. -12 V Solution. If one makes a walk from terminal A towards terminal B and counts the voltages, one gets: V A -E 1 -R 1 *I+E 2 -R 2 *I=V B . We obtain: V A -V B =5+3*1-10+5*1=+3 V Answer D. Problem 3. (two points) Four parallel wires with the same currents are arranged in a perfect square as shown in the figure. Two top wires carry the currents inside the page, while two bottom wires carry the currents outside the page. What is the direction of the magnetic field exactly at the center of the square?
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This note was uploaded on 11/11/2011 for the course PHY 9C taught by Professor Zieve during the Spring '08 term at UC Davis.

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Midterm2Solution - PHYSICS 9C MIDTERM 2 March 3 , 2011 I...

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