. Hawkins electrical guide. Questions, answers & illustrations; a progressive course of study for engineers, electricians, students and those desiring to acquire a working knowledge of electricity and its applications; a practical treatise. ing kept constant-It is very seldom that a circuit is thus balanced unless intentionallybrought about; when this condition exists, the effect is very marked, thepressure rising excessively and bringing great strain upon the insulationof the circuit. Ques. Define critical frequency. Ans. In bringing a circuit to a state of resonance by in-creasing the freque
. Hawkins electrical guide. Questions, answers & illustrations; a progressive course of study for engineers, electricians, students and those desiring to acquire a working knowledge of electricity and its applications; a practical treatise. ing kept constant-It is very seldom that a circuit is thus balanced unless intentionallybrought about; when this condition exists, the effect is very marked, thepressure rising excessively and bringing great strain upon the insulationof the circuit. Ques. Define critical frequency. Ans. In bringing a circuit to a state of resonance by in-creasing the frequency, the current will increase with increasingfrequency until the critical frequency is reached, and then thecurrent will decrease in value for further increase of critical frequency occurs when the circuit reaches thecondition of resonance. ALTERNATING CURRENTS 1,065 Ques. How is the value of the current at the criticalfrequency determined ? Ans. By the resistance of the circuit. Skin Effect.—This is the tendency of alternating currentsto avoid the central portions of solid conductors and to flow orpass mostly through the outer portions. The so-called skineffect becomes more pronounced as the frequency is conductor Fig. 1,306.—Section cf conductor illustrating skin effect or tendency of the alternatingcurrent to distribute itself unequally through the cross section of the conductor as shownby the varied shading flowing most strongly in the outer portions of the conductor. Forthis reason it has been proposed to use hollow or flat conductors instead of solid roundwires. However with frequency not exceeding 100 the skin effect is negligibly small incopper conductors of the sizes usually employed. Where the conductor is large or thefrequency high the effect may be judged by the following examples calculated by ProfessorJ. J. Thomson: In the case of a copper conductor exposed to an electromotive forcemaking 100 periods per second at 1 centimetre from t
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