Variable Capacitor Oscillator
You might (and you should!) remember from some earlier Projects (see Oscillator section) that you can also control the operation of an oscillator by using different capacitor values.
This Project uses a variable capacitor to prove it. After you build the circuit turn the power ON and listen through the Earphone. You'll hear a tone.
Now adjust the Tuning knob to different positions. What do you hear now?
You heard the tone change in pitch from a high frequency to a low frequency (or from low to high frequency). Can you guess why this happens?
If you can't quite figure out the answer, look back at Projects Capacitors and Oscillators and A Variable Capacitor in Capacitor Section along with the notes you made for those two Projects. (See, aren't you glad you kept those notes like we asked you?)