Resistance Of A Unbalanced Wheatstone Bridge Circuit

[AbhiFromXtraZ]

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)?

 

[epenguin]

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 R_g 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 R_g. 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.

 

[AbhiFromXtraZ]

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...

 

[ehild]

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

 

[AbhiFromXtraZ]

Oh Thanks ehild..I will try..

 

[AbhiFromXtraZ]

You mean I need current and emf?...But I have only the resistances...how can I do?

 

[ehild]

Solve symbolically, with emf E. Find the current I_s across the battery in terms of E. The equivalent resistance is R_eq=E/I_s.

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

ehild