## GR0877 Problem 69

**PROBLEM STATEMENT**: *This problem is still being typed*.

**SOLUTION**: (**D**) The impedance of an ideal resistor is , and the impedance of an ideal capacitor is , where is imaginary unit. The total impedance of the circuit is . The total current is . The amplitude of the output voltage is . From this one has . Therefore, when , and when , . The only graph with such a behavior of is (D).

*Found a typo? Comment!*

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Quick way to get this one: the circuit is a low-pass filter, so for low w, Vout=Vin, and Vout goes to zero as w goes to infinity. Only (D) shows this behavior

Exactly. From doing all the practice tests, I can tell you that high and low pass filters comes up a lot. Look at question 39 on the 2001 test for another problem and a great explanation here: http://grephysics.net/ans/0177/39 . In particular, look at the comments for that problem on that site. They helped me a ton.

Exactly!! After reading it I just figured it is low pass or high pass lol

Didn’t any one notice that the equivalent resistance of tandem inductance and capacitor is \omega L – 1/(\omega C)? so the magnitude of V_0 would be 1/(\omega^2 LC-1), with the increase of \omega, V_0 would be infinite when \omega equals \sqrt(1/LC), but the figures of the problem did not show this feature.

OK, I was wrong, I mistook resistor for inductance.