Resistance Of A Unbalanced Wheatstone Bridge Circuit

In summary, you can find the equivalent resistance across the battery (I mean the whole circuit) of a Wheatstone Bridge circuit IF GALVANOMETER CURRENT IS NOT ZERO (i.e. unbalanced circuit) by solving symbolically, with emf E, and then finding the current Is across the battery in terms of E.
  • #1
AbhiFromXtraZ
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Resistance Of An Unbalanced Wheatstone Bridge Circuit

How to find the equivalent resistance across the battery (I mean the whole circuit) of a Wheatstone Bridge circuit IF GALVANOMETER CURRENT IS NOT ZERO (i.e. unbalanced circuit)?
 
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  • #2
AbhiFromXtraZ said:
How to find the equivalent resistance across the battery (I mean the whole circuit) of a Wheatstone Bridge circuit IF GALVANOMETER CURRENT IS NOT ZERO (i.e. unbalanced circuit)?

I presume 'find' means calculate. You need to know the resistance of the galvanometer. (Note that the 'resistance of the galvanometer' may not mean acutally the resistance of the instrument but might be that of the low resistor that is often included in 'shunt' (in parallel) with it. But that's the one you need to know.)

I thought, I may be wrong, they often put a high resistor in series with the instrument. In both cases it takes a low current. But in the second case this current through the galvo is something small in a way you can ignore - your circuit would be like two parallel branches each consisting of two resistors in series.

If nothing is known of the resistance you will just have to call it Rg or something and develop the equations algebraically. Get expressions for all the currents and voltages, put them together for a solution which will be an expression containing Rg. If you get stuck consult your textbook - it is an absolutely standard kind of problem - or else come back here showing what you have done.
 
  • #3
My book's problem is for balanced bridge...And my question is for unbalanced...you just made it complex with galvo...for convenience please replace the galvo with a simple resistance...galvo is not important...circuit is important...and nothing has to be changed here...
 
  • #4
You have a circuit shown in the figure. Using Kirchhoff's rules, determine the current Is flowing out from the voltage source. The emf of the source is E.

ehild
 

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  • #5
Oh Thanks ehild..I will try..
 
  • #6
You mean I need current and emf?...But I have only the resistances...how can I do?
 
  • #7
Solve symbolically, with emf E. Find the current Is across the battery in terms of E. The equivalent resistance is Req=E/Is.

You can also apply delta-star conversion to get the equivalent resistance. http://www.electrical4u.com/delta-star-transformation-star-delta-transformation/

ehild
 

FAQ: Resistance Of A Unbalanced Wheatstone Bridge Circuit

1. What is a Wheatstone bridge circuit?

A Wheatstone bridge circuit is a type of electrical circuit that is used to measure unknown resistance values. It consists of four resistors, arranged in a diamond shape, with a power source connected at two opposite corners and a galvanometer connected at the other two corners. The resistance of the unknown element can be calculated by measuring the voltage across the galvanometer.

2. How does an unbalanced Wheatstone bridge circuit work?

An unbalanced Wheatstone bridge circuit works by using the principle of Kirchhoff's laws. When the bridge is unbalanced, there is a difference in potential between the two sides of the bridge. This creates a current flow through the galvanometer, which can be used to calculate the unknown resistance value using Ohm's law.

3. What factors can cause an unbalanced Wheatstone bridge circuit?

Several factors can cause an unbalanced Wheatstone bridge circuit. These include variations in the resistance of the resistors, fluctuations in the power source voltage, and changes in the temperature of the circuit. Additionally, loose connections or damaged components can also contribute to an unbalanced bridge.

4. How is the resistance of an unbalanced Wheatstone bridge circuit calculated?

The resistance of an unbalanced Wheatstone bridge circuit can be calculated by using the formula R1/R2 = R3/Rx, where R1 and R2 are the known resistances, R3 is the resistance of the galvanometer, and Rx is the unknown resistance. This formula is derived from the principle of Wheatstone bridge balance.

5. What are the applications of an unbalanced Wheatstone bridge circuit?

An unbalanced Wheatstone bridge circuit has several practical applications, including measuring the resistance of unknown elements, detecting small changes in resistance, and determining the conductivity of materials. It is commonly used in electronic circuits, medical equipment, and scientific experiments.

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