In the context of electrical circuits, "A.C. fundamentals" typically refers to alternating current fundamentals. One aspect of alternating current behavior is the concept of the decay of current in certain circuits. Let's explore this topic in more detail.
When an AC circuit contains components like resistors, capacitors, and inductors, the behavior of the current can differ from that in a purely resistive DC circuit. In circuits with capacitors and inductors, the current doesn't immediately reach its steady-state value when the AC voltage is applied or changed. Instead, the current experiences a transition over time, often referred to as the transient response.
Decay of current specifically refers to the behavior of the current in circuits involving capacitors. When an AC voltage is applied across a capacitor, it charges and discharges based on the frequency of the AC signal and the capacitance of the capacitor.
Charging Phase: When the AC voltage is first applied, the capacitor starts charging. As the voltage across the capacitor increases, the current flowing through the circuit decreases. This is because the capacitor is storing energy in the form of an electric field between its plates.
Discharging Phase: As the polarity of the AC voltage reverses, the capacitor discharges. The stored energy in the electric field is released, causing a current to flow in the opposite direction. Again, as the voltage across the capacitor decreases, the current increases.
The process of charging and discharging repeats with each cycle of the AC voltage. However, due to the energy dissipation in the resistor and the limited charge storage capacity of the capacitor, the current in subsequent cycles will be slightly smaller until it reaches a stable amplitude. This gradual decrease in the peak current value over time is referred to as the "decay" of current.
The decay of current in a circuit with a capacitor is more pronounced at higher frequencies. At low frequencies, the capacitor has more time to charge and discharge, resulting in a smaller decay effect.
It's important to note that in circuits with inductors, you would encounter a different behavior. Inductors resist changes in current flow, causing a delay in the establishment of the current when the voltage changes. This is often referred to as "inductive reactance."
In summary, the decay of current is a phenomenon that occurs in AC circuits containing capacitors. It refers to the gradual decrease in the peak current value over successive cycles as the capacitor charges and discharges. This behavior is due to the energy dissipation in the resistor and the finite charging and discharging times of the capacitor.