A radio can tune over the frequency range of a portion of MW broadcast band : (800 kHz to 1200 kHz). If its LC circuit has an effective inductance of 200 `mu H`, what must be the range of its variable capacitor ?

Explanation

`v=(1)/(2pi) sqrt((1)/(LC)), i.e., C=(1)/(4pi^(2)v^(2)L)`
For `L=200muH, v=1200kHz, C=87.9pF`.
For `L=200muH, v=800kHz, C=197.8pF`.
The variable capacitor should have a range of about 88 pF to 198 pF.