(1) In any alternating circuit with a capacitor, the phase of the current leads

Question

(1) In any alternating circuit with a capacitor, the phase of the current leads the phase of voltage by pi/2. Explain why so.


(2) (Hint: What is the definition of impedance?) An RLC series circuit has R=4 Ohms, Xc=3 Ohms and XL=6 ohms. The impedance of this circuit is (please explain your answer)
(A) 5 Ohms
(B) 7 Ohms
(C) 9.8 Ohms
(D) 13 Ohms
(E) 7.8 Ohms


(3) A step-down transformer is used to (please explain your answer)
(A) increase the power
(B) decrease the power
(C) increase the voltage
(D) decrease the voltage
(E) change ac to dc

Explanation / Answer

1) 2) we have Z=sqrt(4^2+(6-3)^2)=5(ohm). 3) decrease the voltage ( since the number of turns is decresed in a step down transformer)

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