- #1
arvindsharma
- 21
- 0
Can someone explain me,why Wheatstone bridge is most sensitive when all four resistances say A,B,C and D are equal?as far as i know condition for Wheatstone Bridge is A/B=C/D.
Wheatstone bridge -- Why set all 4 resistances equal?
- Thread starter arvindsharma
- Start date
In summary, the Wheatstone bridge is most sensitive when all four resistances (A, B, C, and D) are equal. This is because the sensitivity of the bridge is determined by the balance condition of the circuit, which is achieved when R4 is equal to R2 multiplied by R3 divided by R1. When all resistances are equal, this balance condition is easily met, resulting in a higher sensitivity for the circuit. This is due to the fact that the sensitivity is calculated based on the derivative of the current through the galvanometer with respect to any of the four resistances. Therefore, having equal values for all resistances results in a higher sensitivity for the Wheatstone bridge circuit.
- #2
jim hardy
Science Advisor
Gold Member
Dearly Missed
- 9,832
- 4,894
Wheatstone bridges used to employ a galvanometer as a null detector.
Solve the bridge for current through the galvanometer ...
Solve the bridge for current through the galvanometer ...
- #3
zoki85
- 1,198
- 230
arvindsharma said:
Recipe:
From theoretical considerations of the bridge circuit, current through the ideal galvanometer can be understand as function of 4 variables:
IAC=V⋅f(R1,R2,R3,R4)
Definition of the sensitivity is:S=dIAC/dRx
where Rx can stand for any of R1,R2,R3 or R4.Say Rx=R4 and given the condition of the balance R4=R2⋅R3/R1, one searches for the stationary points of multivariable function S by solving the system:
∂S/∂R1=0
∂S/∂R2=0
∂S/∂R3=0
...
∂S/∂R2=0
∂S/∂R3=0
...
- #4
Mike_In_Plano
- 702
- 35
You can vary the thing and still get good results. i.e. the right leg has the same ratio as the left leg is good and sufficient.
To see why the system works better with equal values, find di / dRtest (i in galvenometer) as a function of the values with one value, Rtest set. Then set di/dR to zero to find the maximum sensitivity...
To see why the system works better with equal values, find di / dRtest (i in galvenometer) as a function of the values with one value, Rtest set. Then set di/dR to zero to find the maximum sensitivity...
Related to Wheatstone bridge -- Why set all 4 resistances equal?
1. Why do all four resistances need to be equal in a Wheatstone bridge?
The Wheatstone bridge is a circuit used to measure unknown resistances by comparing it with a known resistance. In order for the bridge to be balanced and provide an accurate measurement, all four resistances need to be equal. This ensures that the voltage across each branch of the bridge is the same, allowing for accurate comparison.
2. Can I use different resistances in a Wheatstone bridge?
While it is recommended to use equal resistances in a Wheatstone bridge, it is possible to use different resistances. However, this may result in inaccurate measurements as the voltage across each branch may not be equal. It is best to use equal resistances to ensure the accuracy of the measurement.
3. What happens if one of the resistances in a Wheatstone bridge is much larger or smaller than the others?
If one of the resistances is significantly larger or smaller than the others, it can throw off the balance of the bridge and result in inaccurate measurements. This is why it is important to use equal resistances in a Wheatstone bridge.
4. Can I use resistors with different values in a Wheatstone bridge?
Yes, as long as all four resistances are equal. This means you can use resistors with different values as long as they are all the same value. For example, you can use four 100-ohm resistors or four 1000-ohm resistors in a Wheatstone bridge.
5. Is it necessary to have four resistances in a Wheatstone bridge?
Yes, a Wheatstone bridge requires four resistances to function properly. The bridge relies on the comparison of two unknown resistances with two known resistances. Without all four resistances, the bridge cannot be balanced and accurate measurements cannot be obtained.
Similar threads
-
Electrical Engineering
-
Electromagnetism
-
Advanced Physics Homework Help
-
Introductory Physics Homework Help
-
Introductory Physics Homework Help
-
Introductory Physics Homework Help
-
Engineering and Comp Sci Homework Help
-
Electrical Engineering
-
Electrical Engineering