Question

the time constant of CR circuit is

Answer 1

Since the time constant (τ) for an RC circuit is the product of resistance and capacitance, we obtain a value of 1 second: If the capacitor starts in a totally discharged state (0 volts), then we can use that value of voltage for a “starting” value. The final value, of course, will be the battery voltage (15 volts).

Answer 2

The time also called the transient response, required for the capacitor to fully charge is equivalent to about 5 time constants or 5T. This transient response time T, is measured in terms of τ = R x C, in seconds, where R is the value of the resistor in ohms and C is the value of the capacitor in Farads.