Question

A variable capacitor with a range from 11 to 506 pF is used with a coil to form a variable-frequency LC circuit to tune the input to a radio. (a) What is the ratio of maximum frequency to minimum frequency that can be obtained with such a capacitor? If this circuit is to obtain frequencies from 0.71 MHz to 2.22 MHz, the ratio computed in (a) is too large. By adding a capacitor in parallel to the variable capacitor, this range can be adjusted. To obtain the desired frequency range, (b) what capacitance in picofarads should be added and (c) what inductance should the coil have?

Answer 1

(a)

Range of variable capacitor is 11 to 506pF.

&

Frequency of a LC circuit ,

The ratio of maximum frequency to minimum frequency is 6.78 [Answer].

(b)

Here, MHz and MHz

Let the capacitance of the additional capacitor= C pF.

Net capacitance with CpF capacitor in parallel=

45.35 pF capacitor should be added in parallel. [Answer]

(c)

The coil should have inductance = [Answer].