Question

1) A capacitor consists of two metal surfaces separated by an electrical insulator with no electrically conductive path through it. Why does a current flow in a resistor-capacitor circuit when the switch is closed?

Answer 1

Current flows in an RC circuit when the switch is closed because a capacitor can store an electrical charge. In an AC circuit, capacitors charge and discharge due to the alternating current, which allows rms current to flow. Capacitive reactance measures the opposition to current flow and changes with the frequency of the AC signal.

Step-by-step explanation:

In a resistor-capacitor (RC) circuit, when the switch is closed, current flows even though a capacitor is essentially an open circuit. This is because a capacitor can store electrical charge temporarily. During the charging phase of a capacitor, charge carriers are moved onto the capacitor plates, creating a current through the resistor connected in series with it. The capacitor continues to charge until the voltage across its plates equals the voltage of the power source.

If an AC voltage is applied, the capacitor will continually charge and discharge in response to the alternating current, allowing for what is known as the rms current to flow in the circuit. This occurs because the voltage across the capacitor in an AC circuit is continually reversing, which causes the capacitor to charge and discharge at the frequency of the AC signal. Capacitive reactance (Xc) is a measure of how much the capacitor opposes the current flow, and this reactance is inversely proportional to the signal frequency.

Answer 2

Current flows in a resistor-capacitor circuit because of the varying electric field across the plates of a capacitor induced by an AC voltage source (displacement current)

Step-by-step explanation:

In a capacitor, current does not flow the same way it does in a circuit, that is through conduction. This is because there is a highly resistive material in between the plates of the capacitor. Rather current flows through a phenomenon called displacement current.

Because of change in charge accumulation with time above the plates, the electric field changes causing the displacement current.

Displacement current arises due to the flow of electrons as a result of the varying magnetic fields set up on the plates of the capacitor when supplied with an AC voltage. It is important to note that a DC voltage does not induce any displacement current.

Through this, phenomenon discovered by Maxwell, current is able to flow in a resistor-capacitor circuit despite the absence of an electrically conductive path through the plates.