1. What is the equivalent resistance of the three resistors on in the

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
C. 3R/2
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
Which of the following equations applies to the circuit in this
A. I1 + I2 + I3 = 0
C. I1 + I2 – I3 = 0
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
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