HYPERPHYSICS  NOTE: THIS HYPER PHYSICS LINK , AC CIRCUITS AND TRANSFORMERS

FINAL EXAM PART 2 SP'12

QUIZ 11   ~   CH. 31

EXERCISES/PROBLEMS: DISCUSSIONS HAVE BEEN  POSTED THIS WEEKEND SO STAY TUNED

TRANSFORMERS: Required on final exam: Problem 35.  The following is a list of extra credit problems that will appear in some form on the final examination (Monday, 5-21-12, noon to 3 pm or 1 pm to 4 pm, RM 1908, regular lecture hall)   Source connected to resistor, current in phase with voltage: Problem 1 Source connected to CAPACITOR,  current leads  voltage by 90 degrees: Problem 4 Source connected to INDUCTOR,  current lags  voltage by 90 degrees:  Problem 5 LRC series circuit: Problems 15, 17 LRC series circuit at RESONANCE: Problems 26, 27

35. STEP DOWN TRANSFORMER:  (a) N2/N1 = V2/V1  = 12.0 (V)/ 120 (V) (2 sig. figs).  Find N1/N2 . Please try to understand the derivation from class notes or the textbook. (b) I2 is an rms (root mean square) value. I2 = I2max/(1.41), where  I2max  is the current amplitude of the oscillation. 1.41... is the square root of 2. See section 31.1. I2 = V2/R, where R = 5.00 ohms and V2 is the rms value of secondary voltage, i.e.,  V2 = V2max/(1.41).  (c) Average Power =  I2 * V2    = (1/2)*I2max*V2max   . The factor of 1/2 comes from averaging a sinusoid over the period of oscillation and is a classic result in electrical engineering . See section 31.1. Note: Average Power =    I2 * V2    = V22/R =I22*R, where R = actual load resistance.  (d)  Average power delivered by source (indexed by 1)  to load  is  P = I1*V1  = I12*R', where R' is some effective resistance. Find R'  and show R'= V1/I1  = R*(N1/N2)2  .    Note R' > R.

THE OTHER PROBLEMS ARE EXTRA CREDIT.  YOU SHOULD BE ABLE TO FIGURE THEM OUT FROM CLASS NOTES, NUMEROUS INTERNET EXAMPLES  AND TEXTBOOK EXAMPLES.  DO YOUR RESEARCH !