(a) in any A.C. circuit, is the applied instantaneous voltage equal to the algebraic sum of the instantaneous voltage

Question

Answer the following questions:

(a) in any A.C. circuit, is the applied instantaneous voltage equal to the algebraic sum of the instantaneous voltage across the series element of the circuit? Is the same true for rms voltage? 

(b) A capacitor is used in the primary circuit of an inductor coil. 

(c) A supplied voltage signal consists of a super position of a D.C voltage and A.C. voltage of high frequency. The circuit consists of an inductor and a capacitor in series. Show that the D.C. signal will appear across C and the A.C. signal across L. 

(d) Why is choke coil needed in the use of florescent tubes with A.C. mains? Why can we not use an ordinary resistor instead of the choke coil?

Answer 1

(a) Yes. The same is not true for rms voltage, because voltage across different element may not be in phase. 

(b) The high induced voltage, when the circuit is broken, is used to change the capacitor, thus avoiding sparks, etc. 

(c) For dc, impedance of L is negligible and C very high (infinite), so the D.C. signal appears across C. For frequency ac, impedance of L is high and that of C is low. So, the A.C. signal appears across L. 

(d) A choke coil reduces voltage across the tube without wasting power. A resister would waste power as heat.