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1. What is the equivalent resistance of the three resistors on in the figure at right A. 3R D. 2R/3 B. 2R E. R/3 R R C. 3R/2 R Two resistor R in parallel give Reff = ½ R. Then, ½ R and R in series à Reff = 3/2 R à correct answer is C 2. Which of the following equations applies to the circuit in this figure A. I1 + I2 + I3 = 0 C. I1 + I2 – I3 = 0 B. D. I1 – I2 + I3 = 0 I1 – I2 – I3 = 0 Consider the node indicated by the red circle in the figure. I1, I2, and I3 are flowing into the node. No current is flowing out of the node. Thus I1+I2+I3=0 à correct answer is A 3. Two copper wires have the same length but the second has half the diameter of the first. If the resistance of the first is 2 ohms, the resistance of the second is A. ½Ω B. 1Ω C. ¼ Ω D. 4 Ω E. 8Ω The resistance of a wire is inversely proportional to its cross-sectional area. The 2nd wire has ½ the diameter, and therefore ¼ of the area. 2/¼ = 8 à correct answer is E 4. V1 is the voltage across R1. Which is correct? Let I be the current. I = V/(R1+R2). Then V1 = IR1 = VR1/(R1+R2) à correct answer is D 5. Consider the circuit to the right. The switch S is closed at time t=0. A very long time later, the potential drop across the capacitor will be: A: ε B: 0 C: depends on the value of R D: depends on the value of C E: depends on the values of R and C Let VC be the voltage across the capacitor. Kirchoff's law for voltage says ε = VC + IR. A long time after the switch is closed, the capacitor is charged and no current flows, ie, I=0. Then the equation above simply becomes ε = VC à correct answer is A