WAEC Physics 2014 Objective — Question 39

Question 39 of 50 from the West African Examinations Council (WAEC) Physics 2014 Objective paper, with the correct answer and a full explanation.

Which of the following conditions occur at resonance in a series RLC circuit? I. Impedance equals resistance II. Current is maximum III. Reactances are maximum IV. Current and Voltage are 90° out of phase

A. I and II onlyCorrect
B. I, II and III only
C. I, II, III and IV
D. II, III and IV only

Explanation

At resonance in a series RLC circuit, impedance equals resistance (minimum impedance) and current is maximum. The inductive and capacitive reactances are equal (not 'maximum'), and current and voltage are in phase (not 90° out of phase), so only I and II are correct.

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