Wheatstone Bridge Questions and Answers – Electrical Measurements

1. What is the relation between the balance equation and the magnitude of input voltage?

Directly proportional

Independent

Inversely proportional

Depends on the null indicator

Answer.2. Independent

Explanation:-

The bridge is in a balanced condition when no current flows through the coil or the potential difference across the galvanometer is zero.

Under Balancing conditions, the unknown resistance R_{x} is given by

R_{x} = (R_{3}R_{1})/R_{2}

From the above equation, the input voltage does not appear in the expression for the balanced equation. Thus balance equation is independent of the magnitude of input voltage.

2. The simplest type of bridge used for the measurement of medium resistances is known as ______

Kelvin

Schering

Anderson

Wheatstone

Answer.4. Wheatstone bridge

Explanation:-

The Wheatstone bridge circuit is used to compare an unknown resistance with a known resistance. The bridge is commonly used in control circuits. The wheat stone bridge is the most accurate method available for measuring resistance and is popular for laboratory use.

The resistance with values ranging from 1Ω to 100Ω is called medium resistance. The resistors employed in electronic circuits usually are of medium resistance type.

This bridge circuit is used to determine medium resistance ranging from approximately an ohm (1Ω) to low mega ohms (MΩ).

Wheatstone bridge is also used to measure the resistance of cables and telephone lines for the locatıon of fault positions. For measuring low resistances, care should be taken to reduce the error in measurement. Resistances of connecting leads and contacts introđuce some errors in measurement. Errors due to connecting leads and contacts can be eliminated when we use Kelvin double bridge.

The other different methods used for measurement of medium resistance are

Ammeter-Voltmeter method

Substitution method

Ohmmeter method

3. The measurement accuracy in a bridge circuit is

Low

Inaccurate

High

Medium

Answer.3. High

Explanation:-

Since the bridge circuit merely compares the value of an unknown component with that of an accurately known component (a standard), its measurement accuracy can be very high. This is because the readout of this comparison is based on the null indication at bridge balance, and is essentially independent of the characteristics of the null detector. The measurement accuracy is, therefore, directly related to the accuracy of the bridge component and not to that of the null detector used.

4. In control applications, one arm of the bridge circuit contains a _______

Capacitive element

Resistive element

Inductive element

Impedance element

Answer.2. Resistive element

Explanation:-

The bridge circuit can be used in the control circuits. When used in such control applications, one arm of the bridge contains a resistive element that is sensitive to the physical parameter like pressure, temperature, etc. which is to be controlled.

5. Accuracy of bridge circuit depends on _______

Component values

Null detector

Voltage source

Current source

Answer.1. Component Value

Explanation:-

Bridge compares the value of an unknown component with that of an accurately known standard component. Thus, the accuracy of the measurement depends on the bridge and not on the null detector.

6. Commonly used D.C. bridges are _______

Schering and Anderson

Maxwell inductance and capacitance

De Sauty’s and Wagner

Wheatstone and Kelvin

Answer.4. Wheatstone and Kelvin

Explanation:-

DC bridges are used to determine the unknown conducting value or sometimes to determine the conductance associated with conducting wires. Wheatstone bridge and Kelvin double bridge are the two types in this category.

Schering Bridge is used for the measurement of Inductance.

De Sauty’s bridge & Schering Bridge is used for the measurement of Capacitance.

7. The bridge circuit can be used in _______

High voltage circuits

Low power circuits

Control circuits

Digital integrated circuits

Answer.3. Control Circuits

Explanation:-

The bridge circuit can be used in the control circuits. When used in such control applications, one arm of the bridge contains a resistive element that is sensitive to the physical parameter like pressure, temperature, etc. which is to be controlled.

8. What happens to the balance condition, if the source and detector are interchanged?

Increases by a factor of 2

Reduces to half

Remains unchanged

Independent of the type of source and detector

Answer.4. Independent of the type of source and detector

Explanation:-

The bridge is balanced either manually or automatically using the output signal from the detector in a feedback loop to find the null position.

Under Balancing conditions, the unknown resistance R_{x} is given by

R_{x} = (R_{3}R_{1})/R_{2}

The null condition is independent of the source resistance, of the voltage source supplying the bridge, or the sensitivity or input resistance, of the detector. These, however, determine the precision with which the balance condition can be determined. Hence the balance condition is independent of the positions of the source and the detector.

9. What is the balanced condition for the given bridge?

Z_{1}R_{3} = R_{2}Z_{4}

Z_{1}R_{2} = R_{2}Z_{3}

Z_{1}R_{4} = R_{2}Z_{3}

R_{3}R_{2} = Z_{1}Z_{4}

Answer.1. Z_{1}R_{3} = R_{2}Z_{4}

Explanation

The bridge is in a balanced condition when no current flows through the coil or the potential difference across the galvanometer is zero.