Question
What is the term for the time required for the capacitor in an RC circuit to be charged to 63.2% of the applied voltage or to discharge to 36.8% of its initial voltage?
Answer Options
- A) An exponential rate of one
- B) One time constant
- C) One exponential period
- D) A time factor of one
Correct Answer: B
Explanation
When a DC voltage is applied to a circuit containing a resistor (R) and a capacitor (C) or a resistor (R) and an inductor (L), the voltage and current do not change instantaneously but follow an exponential curve. This transient period is governed by the values of R and C (or R and L).
This characteristic period is called One time constant (symbolized by \tau). Mathematically, \tau is defined as the time needed for the circuit voltage or current to complete approximately 63.2% of its total change toward its final value (for charging) or to decay to approximately 36.8% of its initial value (for discharging). In an RC circuit, the time constant \tau is simply the resistance value multiplied by the capacitance value (\tau = R \times C).
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