Interview Question for ASIC Engineer at Hewlett-Packard:

The voltage initially begins at 0V and charges to the supply voltage in the shape of an inverse exponential. The shape of the waveform is determined by the resistor and the voltage level at the capacitor. The capacitor is initially at 0V so the current through the resistor is high when the switch initially closes. As the voltage increases at the capacitor the voltage drop over the resistor becomes less which in turn reduces the charging current. This slows the rate of charge hence determining the shape of the voltage waveform over time.