SSC JE Electrical Engineering 2012 Paper

Question : 113 of 200

Marks: +1, -0

A 120 V, 60 W incandescent lamp has to be operated from 220 V, 50 c/s, 1 phase ac supply. In order to do, this a circuit element has to be connected in series with the lamp. Which one of the following series element is preferable ?

Pure capacitance
Pure inductance or capacitance
Resistance
Pure inductance

Validate

Solution:

Series capacitors are generally employed to imporve the stability of the system and to increase the voltage rating.
We know that the reactance of capacitor is given as

R_C = 1/2πf_c

For an AC source, frequency f > 0 ie.

R_C = 1/2xfc <0

which means that capacitor offers a constant resistance in A.C. circuit i.e. it allows the lamp to glow continuously. In case of inductance, the brightness of the lamp will depend upon the number of turns in the inductor

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