# Capacitance, unbalanced wheatstone.

• Suraj M
In summary, the problem involves finding the capacitance across points A and B, where the current is divided into q1 and q2, with the assumption that q2 is greater than q1. The relevant equations are C = Q/V, KVL, KCL, and loop law. The solution involves splitting the current at T into q3 and q2-q3, and using loop law for UPQTU and QRSTQ to obtain a relation between q1, q2, and q3. Using this relation, the equation C_AB = (q2 + q1)/(q1/5 + 10/(q1+q3)) is used to solve for the capacitance, resulting in a value of 155
Suraj M
Gold Member

## Homework Statement

Find capacitance across AB
So i divided the current into q1 and q2 as shown. then i assumed that q₂>q₁.

## Homework Equations

##C=\frac{Q}{V}##
I don't know anything after KVL KCL and loop law.

## The Attempt at a Solution

So i split the current at T into q₃ and q₂-q₃
by the diagram, i used Loop law for UPQTU and QRSTQ.
this gave me a relation between q₁,q₂ and q₃.
i got
$$q₁= 15q₃$$
$$q₂=16q₃$$
$$q₁ = \frac{15}{16} q₂$$
using these, i used the equation..
$$C_{AB} = \frac{q₂ +q₁}{\frac{q₁}{5} + \frac{10}{q₁+q₃}}$$
so i got $$C_{AB} = \frac{155}{23} µF$$
Is this right.? because i doubt it.

You work with charges instead of currents. The net charge should be zero at junctions Q and T.

can't we do it by this method? KCL necessary? I will try.

Suraj M said:
can't we do it by this method? KCL necessary? I will try.
You can, but write charge instead of current. And take into account that the net charge on the connected plates is zero, and the charges on the opposite plates of a capacitor are of opposite sign.

Show your work in detail. Otherwise I can not decide if you got the correct result or not.

## 1. What is capacitance?

Capacitance is the ability of a system to store an electric charge. It is measured in Farads (F) and is represented by the symbol C.

## 2. How is capacitance calculated?

Capacitance can be calculated by dividing the charge (Q) stored on one plate of a capacitor by the potential difference (V) across the two plates. This can be represented by the equation C = Q/V.

## 3. What is an unbalanced Wheatstone bridge?

An unbalanced Wheatstone bridge is a type of electrical circuit used to measure an unknown electrical resistance. It consists of four resistors arranged in a diamond shape with a voltage source and a galvanometer (a device used to detect small electric currents) connected to opposite corners.

## 4. How does capacitance affect an unbalanced Wheatstone bridge?

The capacitance of the circuit can affect the balance of the Wheatstone bridge, as it can create a parallel circuit with the resistors, changing the overall resistance and therefore the balance of the bridge. This can lead to inaccurate measurements.

## 5. How can capacitance be minimized in an unbalanced Wheatstone bridge?

To minimize the effect of capacitance in an unbalanced Wheatstone bridge, the circuit should be designed with minimal distances between components and using shielded cables. Additionally, using a higher frequency AC power source can help reduce the impact of capacitance.

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