Question

A battery, a resistor, and a capacitor are connected in series in an RC circuit. What happens to the current through a resistor after a long time? Explain using Kirchhoff's rules.

Short answer

The behavior of the current through the resistor is that it becomes zero after a long time as the capacitor becomes fully charged. This is explained using Kirchhoff's Voltage Law (KVL) and Ohm's Law.

Step-by-step solution

Understanding the RC Circuit Components

An RC circuit consists of a resistor (R), a capacitor (C), and a battery. The resistor provides resistance to the current flow, the capacitor stores energy in an electric field, and the battery provides a constant voltage (V) across the circuit.

Understanding Kirchhoff's Rules

Kirchhoff's rules consist of two rules that help us understand and analyze electric circuits. The first rule, Kirchhoff's Current Law (KCL), states that the total current entering a junction in a circuit must equal the total current leaving the junction. The second rule, Kirchhoff's Voltage Law (KVL), states that the sum of the voltage drops across all elements in a closed loop must be equal to the voltage supplied by the battery.

Applying Kirchhoff's Voltage Law (KVL) to the RC Circuit

In an RC circuit, we can set up a loop consisting of the battery, the resistor, and the capacitor. According to KVL, the sum of the voltage drops across the resistor (V_R) and the capacitor (V_C) should be equal to the battery voltage (V). V = V_R + V_C

Calculating the Voltage Drop across the Resistor (V_R)

The voltage drop across the resistor can be calculated using Ohm's Law, which states that the voltage across a resistor is directly proportional to the current flowing through it (I) multiplied by the resistance (R). V_R = I * R

Calculating the Voltage Drop across the Capacitor (V_C)

The voltage across a capacitor can be expressed as: V_C = Q / C Where Q is the charge stored on the capacitor.

Determining the Charge on the Capacitor after a Long Time

After a long time, the capacitor becomes fully charged, and the voltage across it (V_C) will be equal to the battery voltage (V). At this point, the capacitor acts as an open circuit, so no current will flow through it.

Calculating the Current through the Resistor after a Long Time

Since the voltage across the capacitor (V_C) is equal to the battery voltage (V) after a long time, there will be no voltage drop across the resistor (V_R). Therefore, according to Ohm's Law (V_R = I * R), the current (I) through the resistor will be zero. In conclusion, after a long time, the current through the resistor becomes zero as the capacitor becomes fully charged. This behavior is explained using Kirchhoff's Voltage Law (KVL) and Ohm's Law.