A radio receiver employs a series RLC tuning circuit with a fixed inductance and…

PHYSICS · Subjective · A Level · Physics · Fields and their consequences · Fields and their consequences

Problem

A radio receiver employs a series RLC tuning circuit with a fixed inductance

L

and variable capacitance

C

. Two nearby stations transmit at carrier frequencies

f_A = 1.002\,\text{MHz}

and

f_B = 1.006\,\text{MHz}

. (a) Explain why the tuning circuit must exhibit a sharp resonance to select station

A

without appreciable interference from station

B

. (b) The circuit can be operated with two different series resistances:

R = 20\,\Omega

and

R = 80\,\Omega

. On separate but identically scaled axes, sketch the current–frequency curves for these two cases and indicate the positions of

f_A

and

f_B

. (c) From your sketches, justify whether decreasing or increasing the resistance improves the selectivity of the receiver, and give the reason for your answer.

Related theory

Power in AC Circuits
AC Circuit Analysis
Resonance in AC Circuits
Series LCR circuit
Alternating Current

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