Question: The RC time constant, also called tau, the time constant (in seconds) of an RC circuit, a irst order RC circuit is composed of one resistor and one capacitor and is the simplest type of RC circuit, and is equal to the product of the circuit resistance (in ohms) and what (in farads)? 
Sentence (from "Pearson–Anson effect"): Since the development of microelectronics, these simple negative resistance oscillators have been superseded in many applications by more flexible semiconductor relaxation oscillators such as the 555 timer IC.
Relevant evidence: No