Answer: 159 kHz.
- A 50 kHz
- B 100 kHz
- C 159 kHz
- D 1000 kHz
Correct answer: C. 159 kHz
Explanation: f0 = 1/(2pi sqrt(LC)) = 1/(2pi sqrt(10-4 x 10-7)) = 1/(2pi x 10-5.5) = 1/(2pi x 3.16 x 10-6) = 106/(2pi x 3.16) = 159 kHz.
In a pure inductor the current lags the voltage by 90° (energy is briefly stored in the magnetic field before current responds); in a pure capacitor the current leads the voltage by 90° (current must flow to build up charge before voltage rises) - the mnemonic "ELI the ICE man" keeps these straight.
Concept context
AC circuits, impedance, LCR series circuit, resonance, transformers, and power factor.