{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

# examPS - Physics 21 Fall 2004 Solution Practice Exam#2...

This preview shows pages 1–2. Sign up to view the full content.

Physics 21 Fall, 2004 Solution, Practice Exam #2 Problem 1. For the following circuit: R L C V rms ( frequency ω ) φ ω L I rms 1/ ω C I rms R I rms V rms (a) Write the loop equation for this circuit. V IR L dI dt Q C =0 (b) If R =20Ω, L =0 . 025 H, and C =50 µ F (50 × 10 6 F), ±nd the frequency ω for which the current lags the volt- age across the inductor by 30 . Hint: Make sure ω> 0 . OOPS, the question SHOULD HAVE SAID, ±nd the frequency ω for which the applied voltage lags the volt- age across the inductor by 30 . From the diagram, the phase angle φ can be written tan φ = ωL 1 ωC R . If the applied voltage V sin( ωt + φ ) lags the voltage across the inductor by 30 , then φ =60 and tan φ = 3= ωL 1 ωC R We transform this into a quadratic equation for ω 2 3 1 /C =0 , whose solution is ω = 3 R ± p 3 R 2 +4 L/C 2 L . We must take the plus sign so that ω> 0; the result is ω =1 . 82 kH. A negative value of ω would reverse the directions of the vertical vectors on the phasor diagram, and change the phase relations. (c) If

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

### Page1 / 2

examPS - Physics 21 Fall 2004 Solution Practice Exam#2...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online