Wheatstone Bridge Questions and Answers – Electrical Measurements

Wheatstone Bridge Questions and Answers – Electrical Measurements

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

  1. Directly proportional
  2. Independent
  3. Inversely proportional
  4. Depends on the null indicator

Answer.1. 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 Rx is given by

Rx = (R3R1)/R2

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 ______

  1. Kelvin
  2. Schering
  3. Anderson
  4. 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

  1. Ammeter-Voltmeter method
  2. Substitution method
  3. Ohmmeter method

 

3. The measurement accuracy in a bridge circuit is

  1. Low
  2. Inaccurate
  3. High
  4. 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 _______

  1. Capacitive element
  2. Resistive element
  3. Inductive element
  4. 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 _______

  1. Component values
  2. Null detector
  3. Voltage source
  4. 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 _______

  1. Schering and Anderson
  2. Maxwell inductance and capacitance
  3. De Sauty’s and Wagner
  4. 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 Capacitacne.

 

7. The bridge circuit can be used in _______

  1. High voltage circuits
  2. Low power circuits
  3. Control circuits
  4. 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?

  1. Increases by a factor of 2
  2. Reduces to half
  3. Remains unchanged
  4. 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 Rx is given by

Rx = (R3R1)/R2

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?

  1. Z1R3 = R2Z4
  2. Z1R2 = R2Z3
  3. Z1R4 = R2Z3
  4. R3R2 = Z1Z4

Answer.1. Z1R3 = R2Z4

Explanation

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

So at the balanced condition

VAC = VA − VC = 0

or

VA = VC

I1 = I2 & I3 = I4

V = V4 + V3 = V1 + V2

Applying Nodal voltage at A & B

Z4 × V/(Z4 + R3) = Z1 × V/(Z1 + R2)

Z1R3 = R2Z4

 

10. The advantages of the bridge circuits is/are

  1. High Accuracy
  2. Used in the control circuit
  3. Balanced conditions remain unchanged
  4. All of the above

Answer.4. All of the above

Explanation:-

Advantages of Bridge Circuit

The various advantages of the bridge circuit are as follows:

1. The measurement accuracy is high because the measurement is done by comparing the unknown value with the standard value.

2. The accuracy is not dependent on the characteristic of a null detector and is dependent on the component value.

3. The balanced equation is independent of the magnitude of the input voltage. These quantities do not appear in the balanced equation expression.

4. The balance condition remains unchanged if the source and detector are interchanged.

5. The balanced equation is independent of the sensitivity of the null detector.

6. The bridge circuit can be used in the control circuit.

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