Wheatstone Bridge Balance Condition Questions and Answers – Electrical Measurements

Wheatstone Bridge Balance Condition Questions & Answers – Electrical Measurements

1. The Wheatstone bridge is said to be balanced when

  1. There is deflection in the galvanometer
  2. The resistance of two arms is twice the resistor of adjacent arms
  3. There is no deflection in the galvanometer
  4. Any of the above

Answer.3. There is no deflection in the galvanometer

Explanation:-

If the resistances forming the four arms of the quadrilateral are so adjusted that on sending current in the closed-loop by the cell, there is no deflection in the galvanometer then Wheatstone Bridge is said to be balanced. In this condition, the ratio of the resistances in any of the two adjacent arms of the quadrilateral is equal to the ratio of the resistances in the remaining two adjacent arms.

 

2. The Wheatstone bridge is also known as

  1. Sensitive Bridge
  2. Resistance Bridge
  3. Deflection Bridge
  4. Resistance Ratio Bridge

Answer.2. Resistance bridge

Explanation:-

The Wheatstone bridge is also known as the Resistance bridge since 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.

 

3. From the given figure what will be the ratio of Wheatstone bridge arms

  1. P/Q = R/S
  2. P/S = R/Q
  3. PQ = RS
  4. PR = QS

Answer.1. P/Q = R/S

Explanation:-

Consider four resistances P, Q, R and S connected in four arms of a parallelogram ABCD.

One part i1 flows in the arm AB and the other part i2 flows in the arm AD.

The resistances P, Q, R, and S are so adjusted that on pressing the key K2, there is no deflection in the galvanometer G. That is, there is no current in the diagonal BD. Thus, the same current I1 will flow in the arm BC as in the arm AB and the same I2, will flow in the arm DC as in the arm AD.

Applying Kirchhoff’s second law for the closed-loop BADB, we have

−i1P + i2R = 0

Pi1  = Ri2 ——–(1)

Similarly, for the closed-loop CBDC, we have

−i1Q + i2S = 0 ———- (2)

Qi1  = Si2

Dividing equation 1  by equation 2

Pi1/Qi=  Ri2/i2S

P/Q = R/S

 

4. Wheatstone bridge consists of ______

  1. 4 resistive arms
  2. 2 resistive arms
  3. 6 resistive arms
  4. 8 resistive arms

Answer.1. 4 Resistance arms

Explanation:-

A Wheatstone bridge circuit in its simplest form consists of a network of four resistance arms forming a closed circuit. A source of current is applied to two opposite junctions. The current detector is connected to the other two junctions as shown in Fig.

The arm consisting of the resistance R1 and R2 are called ratio arms.

The arm consisting of the standard known resistance R3 is called the standard arm and the resistance Rx is the unknown resistance to be measured. The battery is connected between a and c while the galvanometer (current detector) is connected between b and d.

 

5. Wheatstone bridge works on the principle of ________

  1. Full deflection
  2. Partial deflection
  3. No deflection
  4. Null deflection

Answer.4. Null Deflection

Explanation:-

The Wheatstone bridge circuit uses the comparison measurement method and operates on the null-indication principle. A null detector identifies when a given value is zero.

The Wheatstone bridge circuit compares the value of an unknown component with that of an accurately known standard component. Thus the accuracy depends on the bridge components and not on the null indicator.

The Wheatstone bridge is said to be balanced when there is no current through the galvanometer or when the potential difference across the galvanometer is zero.

 

6. The balance condition of a Wheatstone bridge depends on the ________

  1. Ratio of arms R1 and R2
  2. Ratio of arms R3 and R4
  3. Emf source and null detector
  4. Current source and power source

The Wheatstone bridge consists of four resistive arms R1, R2, R3 and R4 together with a source of emf and a null detector.

The galvanometer is used as a null detector. The arm consisting of the resistance R1 and R2 are called ratio arms.

The arm consisting of the standard known resistance R3 is called the standard arm and it can be varied to obtain the balance condition. The resistance R4 is the unknown resistance to be measured. The battery is connected between a and c while the galvanometer is connected between b and d.

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

R4 = (R3R1)/R2

Since the balancing condition of the Wheatstone bridge depends on the ratio of R1 and R2 hence it is called Ratio arms.

 

7. Balance condition can be obtained by _______

  1. Varying the standard resistance R3
  2. Varying the resistance arms R1 and R2
  3. Keeping the unknown resistance R4 constant
  4. By making use of a null detector

Answer.1. Varying the standard resistance R3

Explanation:-

The Wheatstone bridge consists of four resistive arms R1, R2, R3, and R4 together with a source of emf and a null detector.

The galvanometer is used as a null detector. The arm consisting of the resistance R1 and R2 are called ratio arms.

The arm consisting of the standard known resistance R3 is called the standard arm and it can be varied to obtain the balance condition. The resistance R4 is the unknown resistance to be measured. The battery is connected between a and c while the galvanometer is connected between b and d.

 

8. In a Wheatstone bridge a galvanometer is used as a _____

  1. Current source
  2. Voltage source
  3. Null detector
  4. Full detector

A galvanometer is used in a Wheatstone bridge circuit as a null detector underbalanced conditions. When an unknown voltage is compared with a known voltage and a galvanometer is connected in the circuit, when the two voltages are equal, no current will flow through the galvanometer. As it works on the null indication, the results are not dependent on the calibration and characteristics of the galvanometer.

Underbalanced conditions the galvanometer will provide zero reading. Its pointer will stay in its center position marked zero.

 

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9. Resistance R4 in a wheat stone bridge is known as _______

  1. Standard resistance
  2. Unknown resistance to be measured
  3. Resistance arm
  4. Input resistance

Answer.2. Unknown resistance to be measured

Explanation:-

The Wheatstone bridge is a circuit used to compare an unknown resistance with a known resistance. The resistance R4 is the unknown resistance to be measured.

In a practical Wheatstone’s bridge, at least one of the resistance is made adjustable, to permit balancing. When the bridge is balanced, the unknown resistance (normally connected at R4) may be determined from the setting of the adjustable resistor, which is called a standard resistor because it is a precision device having a very small tolerance.

 

10. The opposite two ends of a Wheatstone bridge consist of ________

  1. Voltage and current source
  2. E.m.f and null detector
  3. Resistance and capacitance
  4. Inductance and impedance

Answer.2. EMF and Null detector

Explanation:-

A bridge circuit in its simplest form consists of a network of four resistance arms forming a closed circuit, with a DC source of current applied to two opposite junctions and a current detector connected to two other junctions. The two opposite ends of a Wheatstone bridge circuit consisting of a source of e.m.f and a null detector.

 

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