In 1919, the 18th Amendment to the U.S. Constitution, which prohibited the sale and manufacture of alcohol, was ratified. It went into effect on January 16, 1920âbeginning the era known as Prohibition.
Because time constant calculations are important, and often needed, it is better to make the definition of the time constant (T) in a CR circuit: THE TIME TAKEN FOR THE VOLTAGE ACROSS A CAPACITOR TO INCREASE BY 63.2% OF THE DIFFERENCE BETWEEN ITS PRESENT AND FINAL VALUES.
You control the time constant of this circuit, the time it takes for the voltage across C2 to reach 63.2% of Vcc, by varying the setting of R4. Notice that the transistor inside of the 555 timer IC is connected via pin 7 of the device to the junction between R1 and R3.