Answer: 7958 Hz.
- A 7958 Hz
- B 2500 Hz
- C 1000 Hz
- D 500 Hz
Correct answer: A. 7958 Hz
Explanation: f<sub>0</sub> = 1/(2π√(LC)) = 1/(2π√(4×10⁻³ × 10⁻⁷)) = 1/(2π√(4×10⁻¹⁰)) = 1/(2π × 2×10⁻⁵) = 1/(4π×10⁻⁵) ≈ 7958 Hz.
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.