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Directions (Q. No. 1 to 5):

Read the following text and answer the following questions on the basis of the same:

Tuning a radio set: In essence the simplest tuned radio frequency receiver is a simple crystal set.

Desired frequency is tuned by a tuned coil / capacitor combination, and then the signal is presented to a simple crystal or diode detector where the amplitude modulated signal, is demodulated. This is then passed straight to the headphones or speaker. In radio set there is an LC oscillator comprising of a variable capacitor (or sometimes a variable coupling coil), with a knob on the front panel to tune the receiver.

Capacitor used in old radio sets is gang capacitor. It consists of two sets of parallel circular plates one of which can rotate manually by means of a knob. The rotation causes overlapping areas of plates to change, thus changing its capacitance. Air gap between plates acts as dielectric.

The capacitor has to be tuned in tandem corresponding to the frequency of a station so that the LC combination of the radio set resonates at the frequency of the desired station.

When capacitive reactance \[({{X}_{\operatorname{C}}})\] is equal to the inductive reactance \[({{X}_{\operatorname{L}}})\], then the resonance occurs and the resonant frequency is given by \[{{\omega }_{0}}=\frac{1}{\sqrt{LC}}\] current amplitude becomes maximum at the resonant frequency. It is important to note that resonance phenomenon is exhibited by a circuit only if both L and C are present in the circuit.

Only then do the voltages across L and C cancel each other (both being out of phase) and the Current amplitude is \[\frac{{{V}_{m}}}{R}\], the total source voltage appearing across R.

This means that we cannot have resonance in a RL or RC circuit.

Name the phenomenon involved in tuning a radio set to a particular radio station.

A) Stabilization

B) Ratification                               

C) Resonance

D) Reflection