On and off the switch immediately .
This circuit is known as relaxation oscillator.If u see th resistor are same or equal value because of that pulse width is directly proportional to capacitance and it is derived from Astable multivibrator - only difference is in AMV the resistors are of different value so that pulse is direclty proportional to time constant (tau) = BOTH R AND C and i have connected one ac source to create disturbance in ckt. practically this disturbance is created by noise.
Change the cap value and get the waveform of your pulse width.
