**Electrical Measurements ****MCQs – ****Measurement of Inductance and Capacitance ( ****Electrical Measurements ****) MCQs**

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**Electrical Measurements MCQs – Measurement of Inductance and Capacitance ( Electrical Measurements ) MCQs**

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# Introduction to AC Bridges

**1. In the simplest form, an AC bridge consists of ____________****a) arms, source and a detector**

b) arms and source

c) source and detector

d) arms and detector**Answer: a****Explanation: In its simplest form, an AC bridge consists of four arms, a source for excitation and a null detector. The source is connected across a pair of arms while the detector is connected to the pair of opposite arms.**

**2. Source is ________**

a) dc supply**b) ac supply**

c) mixed mode supply

d) high voltage supply**Answer: b****Explanation: For an AC bridge we require an AC supply as the source of voltage. It supplies AC voltage at the required frequency.**

**3. At high frequency, source consists of ________**

a) amplifiers

b) regulators**c) oscillators**

d) op amps**Answer: c****Explanation: Op amps are basically differential amplifiers. Amplifiers are used in analog circuits for increasing the strength of the signal. Electronic oscillators form sources at high frequencies.**

**4. Commonly used balance detectors for AC bridges are headphones, tuned amplifiers and vibration galvanometers.****a) True**

b) False**Answer: a****Explanation: Headphones, tuned amplifier circuits and vibration galvanometers are used for detecting the balance condition in AC bridges.**

**5. What is the frequency range for a headphone as a detector?**

a) 20 Hz to 20 kHz

b) 10 kHz to 1 MHz

c) 10 MHz to 1 GHz**d) 250 Hz to 4 kHz****Answer: d****Explanation: Headphones can be used as detectors in AC bridges in the low audio frequency range. Low audio frequency range varies from 250 Hz to 4 KHz.**

**6. For single frequency value, the most sensitive detector is ________****a) tuned detector**

b) vibration galvanometer

c) headphone

d) oscillator**Answer: a****Explanation: Vibration galvanometer is used for detecting the balance condition. Oscillator is used as a source of supply voltage. Tuned detector is the most sensitive detector for a single frequency value.**

**7. Tuned detectors are used in the frequency range of ________**

a) 1 Hz to 100 Hz**b) 10 Hz to 100 Hz**

c) 1 kHz to 100 kHz

d) 1 MHz to 100 MHz**Answer: b****Explanation: Tuned amplifier circuits are used as detectors in the low frequency range. Low frequency range usually ranges from 10 Hz to 100 Hz in AC bridges.**

**8. Vibration galvanometers are used for ________**

a) very high frequency

b) very low frequency**c) low audio frequency**

d) high audio frequency**Answer: c****Explanation: Vibration galvanometers are used as detectors in AC bridges for low audio frequency. Low audio frequency ranges from 5 Hz to 1000 Hz.**

**9. AC bridge is an outcome of ________**

a) Kelvin bridge

b) Megger

c) De Sauty bridge**d) Wheatstone bridge****Answer: d****Explanation: Wheatstone bridge is the simplest form of bridge for the measurement of resistance and forms the basis for an AC bridge. Kelvin bridge is used for the measurement of low resistance and a megger is used for the measurement of high resistances.**

**Sources and Detectors**

**1. At very low frequencies in a AC bridge, the source is _________****a) power line**

b) e.m.f

c) galvanometer

d) tuned circuit**Answer: a****Explanation: Galvanometer is used for detecting the balance condition. The power line acts as a source of supply for bridge measurements in an AC bridge circuit at very low frequencies.**

**2. At high frequencies in an AC bridge, the source is _______**

a) tuned amplifiers**b) oscillators**

c) vibration galvanometer

d) high voltage source**Answer: b****Explanation: Tuned amplifiers are used as a source of voltage in AC bridges. Electronic oscillators are used as a source of supply for bridge measurements in an AC bridge circuit at high frequencies.**

**3. The frequency range of a typical oscillator is _______**

a) 1 Hz to 50 Hz

b) 1 kHz to 100 KHz**c) 40 Hz to 125 kHz**

d) 1 MHz to 150 MHz**Answer: c****Explanation: An oscillator has a frequency range slightly above the audio frequency. A typical oscillator has a frequency range of 40 Hz to 125 kHz.**

**4. The power output for a typical oscillator is _______**

a) 1 kW

b) 1 MW

c) 1 mW**d) 7 W****Answer: d****Explanation: Oscillator usually has a low power output. A typical oscillator has a power output of around 7 W.**

Measurement Of Resistance MCQs

**5. The output waveform in an oscillator is _______****a) sinusoidal**

b) cosinusoidal

c) tangential

d) logarithmic**Answer: a****Explanation: AC supply is generally in the form of sinusoidal signal. In an electronic oscillator, output waveform is very close to sinusoidal.**

**6. The output frequency of an oscillator is _______**

a) unstable and fixed**b) stable and adjustable**

c) stable and fixed

d) unstable and variable**Answer: b****Explanation: In an electronic oscillator, the output frequency is stable. It can be determined accurately and is also adjustable.**

**7. The output power of an oscillator is not enough to drive power circuits.**

a) True**b) False****Answer: b****Explanation: Power circuits generally require a low output in order to function. An electronic oscillator provides sufficient output power to drive power circuits.**

**8. Tuned amplifiers can be set to _______**

a) low frequencies

b) high frequencies**c) any frequency**

d) audio frequencies**Answer: c****Explanation: Tuning refers to varying a parameter. Tuned amplifier circuits can be set to any desired frequency.**

**9. Tuned amplifier circuits respond to broad bandwidth at bridge frequency.**

a) True**b) False****Answer: b****Explanation: Amplifiers can be used to detect the balance condition in AC bridges. Tuned amplifier circuits consist of transistors that respond to a narrow bandwidth at the bridge frequency.**

**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**

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

**Z1 Z4 = Z2 Z3**

**where, Z1, Z2, Z3 and Z4 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**

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

**θ1 + θ4 = θ2 + θ3**

**Where,**

**θ1, θ2, θ3 and θ4 are the phase angles of the impedances Z1, Z2, Z3 and Z4.**

**3. Bridge must be balanced for ________**

a) magnitude

b) angle**c) magnitude and angle**

d) power**Answer: c****Explanation: 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****Explanation: 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****Explanation: 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****Explanation: 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**

**Explanation: 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****Explanation: 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.**

**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****Explanation: 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**

**Explanation: Bridge balance is obtained by varying the resistance R3. At balance we get the value of the unknown resistance as Rx =**

^{R1 R3}⁄R2.**3. Impedance Z4 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****Explanation: 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**Explanation: 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****Explanation: 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.**

Measurement Of Resistance MCQs

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

a) R_{x} = R1R3R2**b) R _{x} = R2R3R1**

c) R

_{x}= R2R1R3

d) R

_{x}= R2R1

**Answer: b**

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

**R**

_{x}= R2R3R1**at balance condition.**

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

a) C_{x} = C3R2R1

b) C_{x} = C3R2**c) C _{x} = C3R1R2**

d) C

_{x}= R1R2

**Answer: c**

**Explanation: The value of unknown capacitance is found using the relation C**

_{x}= C3R1R2 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**

**Explanation: 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.**Inductance Comparison Bridge**

**1. Inductance comparison bridge is used to compute _________****a) unknown inductance and resistance**

b) unknown resistance

c) unknown inductance

d) unknown capacitance**Answer: a****Explanation: By making use of an inductance comparison bridge, the values of unknown inductance and its internal resistance can be determined.**

**2. Ratio arms of the bridge consists of _________**

a) pure inductances**b) pure resistances**

c) pure capacitances

d) inductance and capacitance**Answer: b****Explanation: An inductance comparison bridge is basically used to compute the unknown resistance and inductance values. Ratio arms of an inductance bridge consists of pure resistances.**

**3. Value of unknown resistance is found by using which of the following relation?**

a) R_{x} = R1R3R2

b) R_{x} = R2R1R3**c) R _{x} = R2R3R1**

d) R

_{x}= R2R1

**Answer: c**

**Explanation: The inductance comparison bridge mainly consists of pure resistances in its ratio arm. The value of unknown resistance is given by the relation R**

_{x}= R2R3R1.**4. The value of unknown inductance is found by using which of the following relation?**

a) L_{x} = R1L3R2

b) L_{x} = R2R1

c) L_{x} = L3R1**d) L _{x} = R2L3R1Answer: dExplanation: At balance condition in an inductance comparison bridge, the value of unknown inductance is found by using the relation L_{x} = R2L3R1.**

**5. Inductance control is obtained by _________****a) using R _{2}**

b) using R

_{1}

c) using R

_{3}

d) using L

_{x}

**Answer: a**

**Explanation: In an inductance comparison bridge, the resistance R**

_{2}and R_{3}are variable. The value of resistance R_{2}is varied so as to control the inductance of the bridge.**6. Bridge depends on frequency.**

a) True**b) False****Answer: b****Explanation: In an inductance comparison bridge, the balance equation is independent of frequency. As a result the bridge balance condition remains unaffected by variation in the value of frequency.**

**7. Bridge can be used at audio frequency.****a) True**

b) False**Answer: a****Explanation: An inductance comparison bridge can be used for measurement of unknown inductance at a wide range of audio frequencies in the order of a few Hz to KHz.**

**8. Bridge is used for the measurement of _________**

a) high Q factor**b) medium Q factor**

c) low Q factor

d) very low Q factor**Answer: b****Explanation: The inductance comparison bridge is used for the measurement of low Q factor values of the order of 1 to 10. It cannot be used for the measurement of Q factors below 1. As a result, the bridge is used for the measurement of medium Q factor values.**

**Anderson Bridge, Advantages & Disadvantages of Anderson Bridge**

**1. Anderson bridge is used for _________****a) the measurement of self-inductance**

b) the measurement of resistance

c) the measurement of capacitance

d) the measurement of impedance**Answer: a****Explanation: The Anderson bridge is one of the important bridges used for the measurement of self-inductances in terms of standard capacitance value. Resistance is usually measured by making use of a Wheatstone’s bridge or Kelvin’s double bridge.**

**2. Anderson bridge is a modified form of ________**

a) Wheatstone’s bridge**b) Maxwell bridge**

c) Kelvin double bridge

d) Schering bridge**Answer: b****Explanation: The Anderson’s bridge is a modified form of Maxwell’s bridge which is used for the measurement of self-inductances in terms of standard capacitance value. Wheatstone bridge and Kelvin bridge are used for the measurement of medium and low resistances respectively.**

**3. Anderson’s bridge is basically used for ________**

a) measurement of capacitance

b) measurement of resistance**c) measurement of inductance**

d) measurement of voltage**Answer: c****Explanation: Anderson’s bridge is used basically for the precise measurement of self-inductances in terms of a standard capacitance value over a wide range of values.**

**4. Balance equation for computing the inductance is ________**

a) L_{x} = R_{3} R_{5}

b) L_{x} = CR_{5}

c) L_{x} = CR_{3}**d) L _{x} = CR_{3} R_{5}Answer: d**

Explanation: The balance equation for computing the self-inductance in an Anderson’s bridge is given by the equation, Lx = CR3 R5.

where, C is the standard capacitance

R3 and R5 are the known non-inductive resistances.

**5. Which of the following is a balance equation for computing the resistance?****a) R _{1} = ^{R2 R3}⁄_{R4}**

b) R

_{1}=

^{R2}⁄

_{R4}

c) R

_{1}=

^{R3}⁄

_{R4}

d) R

_{1}= R

_{2}R

_{3}

**Answer: a**

**Explanation: The balance equation for computing the resistance in an Anderson’s bridge is given by the equation R1 =**

^{R2 R3}⁄R4.**where, R2, R3 and R4 are the known non-inductive resistances.**

**6. When the capacitor used is imperfect, the inductance value changes.**

a) True**b) False****Answer: b****Explanation: For an imperfect capacitor used in the Anderson bridge, the value of inductance remains unaffected. The value of R _{1} changes.**

**7. Anderson’s bridge is used for the measurement of capacitance.****a) True**

b) False**Answer: a****Explanation: When a calibrated self-inductance is available, the value of unknown capacitance can be computed by making use of Anderson’s bridge.**

**8. Anderson’s bridge is used for the measurement of ________****a) capacitance**

b) resistance

c) inductance

d) impedance**Answer: a****Explanation: Anderson’s bridge is used for the measurement of capacitance. Unknown capacitance value can be measured accurately in terms of the self-inductance of one of the ratio arms of the bridge.**

**9. Anderson’s bridge makes use of a variable capacitance.**

a) True**b) False****Answer: b****Explanation: An Anderson’s bridge makes use of a fixed capacitance value. Most of the other AC bridges used for the measurement of either capacitance, inductance or impedance make use of a variable capacitance.**

**10. Anderson’s bridge is very basic.**

a) True**b) False****Answer: b****Explanation: An Anderson’s bridge is basically used for the measurement of unknown capacitance value in terms of the self-inductance of one of the standard ratio arms. It is a complex bridge comprising of equivalent star-delta networks for computation of resistance and inductance.**

**11. Bridge balance equations are ________**

a) easy to derive

b) independent of the components**c) complex in nature**

d) real in nature**Answer: c****Explanation: An Anderson’s bridge is basically used for the measurement of unknown capacitance value in terms of the self-inductance of one of the ratio arms. It consists of real as well as complex terms. It also comprises of star-delta equivalent networks for impedance computations.**

**12. Components in an Anderson’s bridge are ________**

a) less

b) zero

c) intermediate**d) more****Answer: d****Explanation: An Anderson’s bridge is a complex type of bridge used basically for the measurement of unknown capacitance. It consists of several resistances, inductances and capacitances in the ratio arms.**

**13. Anderson’s bridge ________****a) can’t be shielded**

b) can be fully shielded

c) can be partially shielded

d) can be shielded based on the components used**Answer: a****Explanation: An Anderson’s bridge is a complex circuit and a modified form of the Maxwell bridge. An Anderson’s bridge cannot be shielded due to the presence of an additional junction point.**

**14. What is the significance of Anderson bridge with respect to Q factor?**

a) difficult to balance the bridge**b) easy to balance the bridge**

c) intermediate balance can be achieved

d) no balance can be done**Answer: b****Explanation: An Anderson’s bridge is a modified form of the Maxwell bridge and is used for the measurement of unknown capacitance in terms of self-inductance of standard value. It is easy to achieve balance condition in an Anderson bridge.**

**15. An Anderson’s bridge can be used to ________**

a) measure mutual inductance

b) measure impedance**c) measure self inductance**

d) measure stray capacitance**Answer: c****Explanation: An Anderson bridge can be used for the measurement of the self-inductance of a coil. A coil with unknown capacitance can be used to determine its self-inductance by making use of an Anderson bridge.**