Answer Happy

Use the circuit of Figure 2.100, p. 70 for this problem. For t his problem, however, the voltage
source value (call it Vs ) is u nknown, but the value of vo is known to be 1.5 V. W e w ish to find the
value of the source voltage Vs .
Sequentially use one or more of the 3 circuit analysis laws, resistor combinations, and voltage or
current division to find more and more voltages and currents in the circuit until you can find the
value of Vs . H int: the first step is to find the current flowing through the 30 Ω resistor. Define
current and voltage variables (with references) on the circuit diagram as necessary.
Think of this problem as a "traceback" check where the original problem gav e the value of Vs
along with all of the resistor values and you were to find the value for Vo . U sing some circuit
analysis technique (which technique does not matter), you obtained the answer of Vo = 1. 5 V.
Now y ou want to check your answer for Vo . Y ou do this by "forgetting" the value that was given
for Vs (treating it as the quantity to be found), and using Vo = 1. 5 V as t he "given" (along with all
the resistance values). After you find the value for Vs in this way, y ou compare it to the value
originally given f or Vs ; if t he values match, you have successfully checked your answer for the
original problem (finding Vo ). If they d on’t m atch, you have made a mistake ( maybe several!)
somewhere along the way.
Note: t he value of Vs for Vo = 1. 5 V i s not 20 V
7. Use the circuit of Figure 2.100, p. 70 for this problem. For this problem, however, the voltage source value (call it V,) is unknown, but the value of v, is known to be 1.5 V. We wish to find the value of the source voltage Vs. Sequentially use one or more of the 3 circuit analysis laws, resistor combinations, and voltage or current division to find more and more voltages and currents in the circuit until you can find the value of Vs. Hint: the first step is to find the current flowing through the 30 N resistor. Define current and voltage variables (with references) on the circuit diagram as necessary. Think of this problem as a "traceback" check where the original problem gave the value of Vs along with all of the resistor values and you were to find the value for V.. Using some circuit analysis technique (which technique does not matter), you obtained the answer of V. = 1.5 V. Now you want to check your answer for V.. You do this by "forgetting" the value that was given for V, (treating it as the quantity to be found), and using V. = 1.5 V as the "given" (along with all the resistance values). After you find the value for V, in this way, you compare it to the value originally given for V,; if the values match, you have successfully checked your answer for the original problem (finding V.). If they don't match, you have made a mistake (maybe several!) somewhere along the way. = 0 = Note: the value of V, for V. = 1.5 V is not 20 V. S
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