Electrical Measurements & Measuring Instruments Multiple Choice Questions on “Bridge Balance Equation”.

1. Bridge balance equation for magnitude is given by which of the following relation?

a) Z_{1} Z_{4} = Z_{2} Z_{3}

b) Z_{1} Z_{2} = Z_{3} Z_{4}

c) Z_{2} Z_{4} = Z_{1} Z_{3}

d) Z_{1} Z_{3} = Z_{2} Z_{4}

Answer: a

Clarification: In an AC bridge, the balance condition for magnitude is given by the equation

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

where, Z_{1}, Z_{2}, Z_{3} and Z_{4} are the impedance arms of the AC bridge circuit.

2. Angular balance equation is given by which of the following relation?

a) θ_{1} × θ_{4} = θ_{2} × θ_{3}

b) θ_{1} + θ_{4} = θ_{2} + θ_{3}

c) θ_{2} + θ_{4} = θ_{1} + θ_{3}

d) θ_{2} × θ_{4} = θ_{1} × θ_{3}

Answer: b

Clarification: The angular balance condition in an AC bridge is given by the relation

θ_{1} + θ_{4} = θ_{2} + θ_{3}

Where,

θ_{1}, θ_{2}, θ_{3} and θ_{4} are the phase angles of the impedances Z_{1}, Z_{2}, Z_{3} and Z_{4}.

3. Bridge must be balanced for ________

a) magnitude

b) angle

c) magnitude and angle

d) power

Answer: c

Clarification: The ratio arms consist of impedances which have magnitude as well as phase. In an AC bridge, balance condition implies magnitude balance as well as angular balance.

4. Phase angle is based on _______

a) source

b) detector

c) power

d) impedance

Answer: d

Clarification: The four ratio arms comprise of impedances which consist of not only magnitude but some phase as well. Value of the phase angles are based on the component of individual impedances.

5. For inductive impedances, the phase angle is _______

a) positive

b) negative

c) zero

d) exponential

Answer: a

Clarification: The current through an inductor does not increase instantaneously. For inductive impedances, the voltage leads the current and as a result the phase angle is positive.

6. For capacitive impedances, the phase angle is _______

a) tangential

b) negative

c) positive

d) logarithmic

Answer: b

Clarification: The voltage across a capacitor does not rise instantaneously. For capacitive impedances, the current leads the voltage and as a result the phase angle is negative.

7. Bridge balance equation for magnitude in terms of admittances is given by the relation.

a) Y_{1}Y_{3} = Y_{2}Y_{4}

b) Y_{1}Y_{2} = Y_{3}Y_{4}

c)Y_{1}Y_{4} = Y_{2}Y_{3}

d) Y_{1} Y_{3} = Y_{2} Y_{4}

Answer: c

Clarification: Admittance is the reciprocal of impedance. The balance condition for magnitude is given by the equation

8. When a bridge is balanced?

a) no voltage drop across the circuit

b) power dissipation is high

c) temperature of the circuit is high

d) no current flows

Answer: d

Clarification: At balance condition, no current flows through the headphones present in the AC bridge circuit. As a result the detector indicates null deflection at balance condition.

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