Electrical Measurements & Measuring Instruments Multiple Choice Questions on “Capacitance Comparison Bridge”.

1. In a capacitance bridge, the arms are _________

a) resistive

b) capacitive

c) inductive

d) mixture of resistance, capacitance and inductance

Answer: a

Clarification: The capacitance bridge is mainly used for the measurement of unknown capacitance. The ratio arms in a capacitance bridge are resistive in nature.

2. How is the bridge balanced?

a) using resistance R_{1}

b) using resistance R_{3}

c) through capacitance C_{3}

d) through capacitance C_{x}

Answer: b

Clarification: Bridge balance is obtained by varying the resistance R_{3}. At balance we get the value of the unknown resistance as R_{x} = ^{R1 R3}⁄_{R2}.

3. Impedance Z_{4} consists of _________

a) resistance R_{x}

b) capacitance C_{x}

c) combination of capacitance Cx and resistance Rx

d) consists of a detector

Answer: c

Clarification: Ratio arm Z_{4} consists of the unknown impedance. Impedance Z_{4} consists of capacitance C_{x} in series with a leakage resistance R_{x}.

4. Impedance Z_{3} consists of_________

a) resistance R_{3}

b) capacitance C_{3}

c) vibration galvanometer

d) capacitance C_{3} in series with resistance R_{3}

Answer: d

Clarification: Impedance usually refers to the combination of resistance and either capacitance or inductance. As we are considering the case of capacitance measurement, impedance Z_{3} comprises capacitance C_{3} in series with resistance R_{3}.

5. Unknown capacitance value is obtained by _________

a) comparison with standard

b) using a tuned detector

c) using capacitance of other ratio arms

d) using a vibration galvanometer

Answer: a

Clarification: Tuned circuit is used for detecting balance condition. Vibration galvanometer is used for the same purpose. Unknown value of capacitance is obtained by comparing it with a standard value.

6. Unknown resistance is obtained by using which of the following relation?

a) R_{x} = (frac{R_1 R_3}{R_2})

b) R_{x} = (frac{R_2 R_3}{R_1})

c) R_{x} = (frac{R_2 R_1}{R_3})

d) R_{x} = (frac{R_2}{R_1})

Answer: b

Clarification: The value of the unknown resistance is obtained by using the relation

R_{x} = (frac{R_2 R_3}{R_1})

at balance condition.

7. Unknown capacitance is found by using which of the following relation?

a) C_{x} = (frac{C_3 R_2}{R_1})

b) C_{x} = (frac{C_3}{R_2})

c) C_{x} = (frac{C_3 R_1}{R_2})

d) C_{x} = (frac{R_1}{R_2})

Answer: c

Clarification: The value of unknown capacitance is found using the relation C_{x} = (frac{C_3 R_1}{R_2}) at balance condition.

8. Actual balance condition can be obtained by _________

a) varying R_{1}

b) varying R_{3}

c) varying R_{2}

d) varying R_{1} and R_{3}

Answer: d

Clarification: Resistances R_{1} and R_{3} are variable, while resistance R_{2} is fixed. By varying the resistances R_{1} and R_{3}, we get the actual balance condition.

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