Consider the circuit shown in the figure . Suppose R1 = 8.0 , R2 = 14 , R3 = 26
ID: 2065505 • Letter: C
Question
Consider the circuit shown in the figure . Suppose R1 = 8.0 , R2 = 14 , R3 = 26 , C = 71 F, and E = 15 V.
http://session.masteringphysics.com/problemAsset/1126230/3/5416321082_85.jpg
A) Find the time constant.
= ____ ms
B) Find the initial current for this circuit.
I = _____ A
C) It is desired to increase the time constant of this circuit by adjusting the value of resistance R1. Should the resistance of this resistor be increased or decreased to have the desired effect?
Someone please walk me through the steps please??
Explanation / Answer
Total resistance is 11.9 ohms Potential difference is 15V Max current is V/R = I = 1.26 A L/R = 0.63(V/R) = 0.79 seconds which is the time constant. multiply it by total R to get inductance which is L = 9.45 H (FYI, dont know if you need that) So at time = 0, as soon as the switch is thrown, the current doesnt just jump to some number. At time zero the current is also at zero. In order to increase the time constant using the resistor you must decrease the resistance. As resistance goes to infinity the time constant gets smaller and smaller and goes to zero. You can prove this by simply making a fraction and increasing or decreasing the denominator of the fraction. Since the time constant is denoted as L/R that will give you a direct answer.