Physicists claim that charge never flows through an ideal capacitor. Yet when an uncharged capacitor is first placed in series with a resistor and a battery, then current flows through the battery and the resistor. Explain how this is possible.
Current cannot flow through the insulator that separates the conductors in a capacitor. Instead, the battery acts as a pump that grabs charge from one plate of a capacitor and shoves it through the resistor and onto the other plate of the capacitor. In this way current can flow though the wires, the battery, and the resistor during the period of time the capacitor is charging but not directly between the capacitor plates.
When an uncharged capacitor is initially placed in series with a resistor and a battery, current flows through the circuit. This may seem contradictory to the claim that charge does not flow through an ideal capacitor. However, the reason behind this lies in the behavior of the capacitor during the charging process.
To understand how current flows in this circuit, let's examine the steps involved:
1. When the circuit is first closed, electrons begin to flow from the negative terminal of the battery through the resistor towards the uncharged capacitor.
2. As the electrons flow through the resistor, they encounter resistance which causes a voltage drop. This voltage drop across the resistor creates an electric field.
3. The electric field created by the voltage drop causes electrons to accumulate on one plate of the capacitor, and an equal number of electrons are repelled from the other plate.
4. As the electrons are forced onto one plate of the capacitor, it becomes negatively charged, while the other plate becomes positively charged, due to the lack of electrons.
5. As the voltage across the capacitor gradually increases, the electric field between the plates becomes stronger, opposing the flow of electrons.
6. Eventually, the voltage across the capacitor reaches the same value as the battery voltage, resulting in equilibrium. At this point, the capacitor is considered fully charged.
7. Once the capacitor is fully charged, the electric field between the plates becomes so strong that it prevents any further flow of electrons from the battery.
Therefore, while current initially flows through the battery and the resistor when the uncharged capacitor is placed in series, this current gradually decreases as the capacitor becomes charged.
It's important to note that in an ideal capacitor, which is an idealized component used for theoretical analysis, there is no physical flow of charge between the plates. Instead, the capacitor stores the charge on its plates in the form of electric potential energy.