JEE Challenger
More from Electrostatic Potential and Capacitance

Energy Stored and Dissipated in Single Step RC Charging Process

Comprehension Passage

PARAGRAPH 1

Consider a simple RCRC circuit as shown in Figure 1.

Process 1: In the circuit the switch SS is closed at t=0t = 0 and the capacitor is fully charged to voltage V0V_0 (i.e., charging continues for time T≫RCT \gg RC). In the process some dissipation (EDE_D) occurs across the resistance RR. The amount of energy finally stored in the fully charged capacitor is ECE_C.

Process 2: In a different process the voltage is first set to V03\frac{V_0}{3} and maintained for a charging time T≫RCT \gg RC. Then the voltage is raised to 2V03\frac{2V_0}{3} without discharging the capacitor and again maintained for a time T≫RCT \gg RC. The process is repeated one more time by raising the voltage to V0V_0 and the capacitor is charged to the same final voltage V0V_0 as in Process 1.

These two processes are depicted in Figure 2.

For Process 1, the relationship between the energy ECE_C stored in the capacitor and the heat energy EDE_D dissipated across the resistor is given by:

Question Diagram 1

Options

A

EC=EDE_C = E_D

Correct
B

EC=EDln⁡2E_C = E_D \ln 2

C

EC=12EDE_C = \frac{1}{2} E_D

D

EC=2EDE_C = 2 E_D

Step-by-Step Solution

In Process 1, a capacitor of capacitance CC is charged by a battery of constant voltage V0V_0 from an initial uncharged state (q=0q = 0) to a fully charged state (q=CV0q = C V_0).

  1. Work Done by the Battery (WbatteryW_{\text{battery}}): The total charge that flows through the battery during the charging process is: Q=CV0Q = C V_0 The work done by the battery maintained at constant potential V0V_0 is given by: Wbattery=QV0=(CV0)V0=CV02W_{\text{battery}} = Q V_0 = (C V_0) V_0 = C V_0^2

  2. Energy Stored in the Capacitor (ECE_C): The electrostatic potential energy stored in the capacitor when fully charged to potential V0V_0 is: EC=12CV02E_C = \frac{1}{2} C V_0^2

  3. Energy Dissipated across the Resistor (EDE_D): By the law of conservation of energy, the difference between the total energy supplied by the battery and the energy stored in the capacitor is dissipated as heat across the resistor: ED=Wbattery−ECE_D = W_{\text{battery}} - E_C ED=CV02−12CV02=12CV02E_D = C V_0^2 - \frac{1}{2} C V_0^2 = \frac{1}{2} C V_0^2

  4. Relationship between ECE_C and EDE_D: Comparing the expressions for ECE_C and EDE_D: EC=12CV02andED=12CV02E_C = \frac{1}{2} C V_0^2 \quad \text{and} \quad E_D = \frac{1}{2} C V_0^2 EC=EDE_C = E_D

This corresponds to Option A.