Question:

charge stored in capacitors


If the total charge stored in capacitors is equal to 100μc, then find the value of x. (10V)

Updated On: Mar 20, 2025
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Solution and Explanation

Understanding the Problem

We are given three capacitors connected in parallel, with capacitances 5 μF, x μF, and 2 μF. The total charge stored is 100 μC when a potential difference of 10 V is applied. We need to find the value of x.

Solution

1. Use the Formula for Total Capacitance in Parallel:

When capacitors are connected in parallel, the total capacitance \( C_{\text{eq}} \) is the sum of the individual capacitances:

\( C_{\text{eq}} = C_1 + C_2 + C_3 \)

Given \( C_1 = 5 \, \mu\text{F} \), \( C_2 = x \, \mu\text{F} \), and \( C_3 = 2 \, \mu\text{F} \), we have:

\( C_{\text{eq}} = 5 + x + 2 = (7 + x) \, \mu\text{F} \)

2. Use the Formula for the Charge Stored in a Capacitor:

The charge stored on the capacitors is given by the formula:

\( Q = C_{\text{eq}} V \)

From the problem, we know that the total charge \( Q = 100 \, \mu\text{C} \) and \( V = 10 \, \text{V} \). Substituting the values into the equation:

\( 100 = (7 + x) \times 10 \)

3. Solve for x:

\( 100 = 70 + 10x \)

\( 10x = 100 - 70 = 30 \)

\( x = \frac{30}{10} = 3 \)

Corrected Final Answer

Thus, the value of \( x \) is \( 3 \).

Note: The original calculation had an error in summing the constant terms.

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Concepts Used:

Electrostatic Potential and Capacitance

Electrostatic Potential

The potential of a point is defined as the work done per unit charge that results in bringing a charge from infinity to a certain point.

Some major things that we should know about electric potential:

  • They are denoted by V and are a scalar quantity.
  • It is measured in volts.

Capacitance

The ability of a capacitor of holding the energy in form of an electric charge is defined as capacitance. Similarly, we can also say that capacitance is the storing ability of capacitors, and the unit in which they are measured is “farads”.

Read More: Electrostatic Potential and Capacitance

The capacitor is in Series and in Parallel as defined below;

In Series

Both the Capacitors C1 and C2 can easily get connected in series. When the capacitors are connected in series then the total capacitance that is Ctotal is less than any one of the capacitor’s capacitance.

In Parallel

Both Capacitor C1 and C2 are connected in parallel. When the capacitors are connected parallelly then the total capacitance that is Ctotal is any one of the capacitor’s capacitance.