A simple tuning circuit consists of what two components connected in parallel?

In a simple tuning circuit, the combination of a variable capacitor and an inductor in parallel is essential for selecting specific frequencies. This configuration allows for resonating at a particular frequency by adjusting the capacitance through the variable capacitor while the inductor serves to create the oscillating electric and magnetic fields necessary for resonance.

When the values of the inductor and the variable capacitor are precisely tuned, they can establish a resonant circuit, which is fundamental in applications such as radio receivers. This tuning mechanism is critical for filtering specific frequency signals and eliminating unwanted frequencies.

Other options, while they include components common in electrical circuits, do not serve the correct purpose for a simple tuning circuit. For example, a variable resistor with a capacitor does not effectively tune to frequencies. An inductor paired with a diode does not form a tuning circuit, as a diode primarily rectifies current rather than tuning it. Lastly, while capacitors and transformers are essential components in electrical circuits, transformers are not typically part of basic tuning circuits.