When we tune in any desired station in a radio receiver by rotating the tuning control we vary

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Question

This question was previously asked in

URSC ISRO Technical Assistant Electronics 24 March 2019 Official Paper

Answer 1

Variable capacitors are used with inductor coils in tuning circuits of radios, television sets, and a number of other devices to allow desired frequencies to pass and attenuate the rest.
In the circuit below, a variable capacitor is connected to a simple antenna circuit.

F1 S.B Deepak 06.03.2020 D7

Transmitted radio waves cause an induced current to flow in the antenna sending an electron flow to the capacitor.
The variable capacitor is used to equalize the inductive and capacitive reactance.
The condition in which the reactances are equalized is called resonance.
The particular frequency that is isolated by the equalized reactance is called the resonant frequency.
This radio circuit is therefore tuned by adjusting the capacitance of the variable capacitor to equalize the inductive and capacitive reactance for the desired resonant frequency,