$($Figure $1)$ shows the circuit for a simple sawtooth oscillator. At time $\backslash ($ t$=0\backslash ),$ its switch S is closed. The neon bulb has initially infinite resistance until the voltage across it reaches $90\mathrm{.}0$ V $,$ and then it begins to conduct with very little resistance $($essentially zero$).$ It stops conducting $($its resistance becomes essentially infinite$)$ when the voltage drops down to $55\mathrm{.}0$ V