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.
The voltage on a discharging capacitor, with time constant T, and initial voltage Vo, varies with time exponentially as; V(t) = Voe^-t/T. So the voltage after one time constant is; V(T) = Vo/e (about 46% of Vo) The Charging eq is; V(t) = Vo[1 - e^-t/T] The voltage after one time constant is; V(T) = Vo[1-1/e] (about 54% of Vo) Since e=2.718 it is common practice to approximate this as ~ 3. Then the discharge voltage afer one time constant is approximately (1/3)Vo And the charging voltage after one time constant is approximately (2/3)Vo