What electronic circuit uses a tapped coil in parallel with a capacitor to control the AC frequency of a circuit?

What electronic circuit uses a tapped coil in parallel with a capacitor to control the AC frequency of a circuit?

• A. Hartley Oscillator
• B. Low-pass
• C. Crystal-controlled Oscillator
• D. Filtering

Answer: (A)

The key idea is that the frequency of an oscillator is set by a resonant LC tank, and the tapped inductor provides the needed feedback to sustain that oscillation. When a coil is tapped and connected in parallel with a capacitor, the two coil sections (L1 and L2) plus the capacitor form a resonant circuit. The oscillation frequency is determined by the total inductance (L1 + L2) together with the capacitance, via f = 1/(2π√((L1+L2)C)). The tap supplies a portion of the output back to the active device, meeting the feedback requirement to maintain steady oscillations. This configuration is the hallmark of a Hartley oscillator. The other options don’t describe this setup: a low-pass stage isn’t an oscillator, a crystal-controlled oscillator uses a crystal instead of a tapped coil, and “filtering” refers to signal shaping rather than producing a sustained AC frequency.

The key idea is that the frequency of an oscillator is set by a resonant LC tank, and the tapped inductor provides the needed feedback to sustain that oscillation. When a coil is tapped and connected in parallel with a capacitor, the two coil sections (L1 and L2) plus the capacitor form a resonant circuit. The oscillation frequency is determined by the total inductance (L1 + L2) together with the capacitance, via f = 1/(2π√((L1+L2)C)). The tap supplies a portion of the output back to the active device, meeting the feedback requirement to maintain steady oscillations.

This configuration is the hallmark of a Hartley oscillator. The other options don’t describe this setup: a low-pass stage isn’t an oscillator, a crystal-controlled oscillator uses a crystal instead of a tapped coil, and “filtering” refers to signal shaping rather than producing a sustained AC frequency.