300+ REAL TIME Electrical Measurements Objective Questions & Answers 2023

Electrical Measurements & Measuring Instruments Multiple Choice Questions on “Qmeter”.

1. Q factor is called __________
a) Quality factor
b) Quantity factor
c) Queen factor
d) Quarter factor
Answer: a
Clarification: Q factor is also known as Quality factor or storage factor. It is basically a ratio of the power stored in an element to the power dissipated in that element.

2. Q factor is also defined as the ratio of _______
a) resistance to reactance
b) reactance to resistance
c) power to voltage
d) current to power
Answer: b
Clarification: Q factor can also be obtained as the ratio of reactance to resistance of an element. For inductive element it is the ratio of X_L to R and for a capacitive element it is the ratio of X_C to R.

3. What is a Q meter?
a) quality meter
b) quantity meter
c) instrument
d) detector
Answer: c
Clarification: Q meter is basically an instrument that is used for the measurement of electrical properties of capacitors and coils. It is also used as a laboratory instrument.

4. Q meter works on the principle of _______
a) barkhausen criterion
b) piezoelectric effect
c) parallel resonance
d) series resonance
Answer: d
Clarification: Q meter basically operates on the characteristics of a series resonant coil. In a series resonant circuit the voltage drop across the coil or a capacitor is equal to the applied voltage multiplied by its Q factor.

5. Q factor for a series resonant circuit is?
a) Q = (frac{X_L}{R} = frac{X_C}{R})
b) Q = X_L R = X_C R
c) Q = (frac{R}{X_L} = frac{R}{X_C})
d) Q = (frac{1}{R})
Answer: a
Clarification: Q factor in a series resonant circuit is given by the relation,
Q = (frac{X_L}{R} = frac{X_C}{R})
where, R is resistance of the coil
X_C is the capacitive reactance
X_L is the inductive reactance.

6. What is the relation between Q factor and voltage?
a) Q = (frac{1}{E})
b) Q = (frac{X_L}{R}=frac{X_C}{R}=frac{E_C}{E})
c) Q = E
d) Q = (frac{R}{X_L}=frac{R}{X_C}=frac{E}{E_C})
Answer: b
Clarification: The applied voltage E is inversely proportional to the Q factor of a circuit and is given by the relation,
Q = (frac{X_L}{R}=frac{X_C}{R}=frac{E_C}{E}).

7. A practical Q meter consists of __________
a) Wien bridge oscillator
b) AF oscillator
c) RF oscillator
d) Crystal oscillator
Answer: c
Clarification: Practically a Q meter consists of a wide range RF oscillator with a frequency range of 50 kHz to 50 MHz. Oscillator acts as a source and delivers current to a low shunt resistance.

8. Voltage across the shunt is measured by ________
a) voltmeter
b) multimeter
c) thermocouple
d) thermometer
Answer: c
Clarification: A thermocouple is used for measuring the voltage across a shunt resistance in a practical Q meter. Electronic voltmeter is used for the measurement of voltage across a resonant capacitor.

9. Inductance of the coil is ________
a) L = (frac{1}{(2πf)C})
b) L = (frac{1}{(2πf)^2})
c) L = (frac{1}{C})
d) L = (frac{1}{(2πf)^2 C})
Answer: d
Clarification: Coil inductance in a Q meter is given by the relation,
L = (frac{1}{(2πf)^2 C})
where, f is the frequency in Hz
C is the capacitance in F.

Electrical Measurements & Measuring Instruments Multiple Choice Questions on “Sensitivity of Wheatstone Bridge”.

1. When the bridge is balanced, what is the current flowing through the galvanometer?
a) 0
b) depends on the ratio arms R₁ and R₂
c) varies by a factor of 2
d) depends on the type of null detector used
Answer: a
Clarification: Under bridge balance condition, no current flows through the galvanometer. Current flow is independent of the values of ratio arms R₁ and R₂.

2. Amount of deflection of the galvanometer depends on _________
a) resistance of the ratio arms
b) sensitivity
c) current flowing through the bridge
d) emf across the circuit
Answer: b
Clarification: The amount of deflection of the galvanometer depends upon its sensitivity. Resistance of the ratio arms does not affect the amount of deflection of the galvanometer.

3. Sensitivity is defined as _________
a) amount of voltage per unit current
b) amount of power per unit voltage
c) amount of resistance per unit voltage
d) amount of deflection per unit current
Answer: d
Clarification: Sensitivity is expressed as

Thus sensitivity is defined as the amount of deflection per unit current.

4. Sensitivity is expressed in _________
a) cm/A
b) m/mA
c) mm/µA
d) inch/nA
Answer: c
Clarification:

where, deflection is in mm and current is in µA.
So the unit of sensitivity is mm/ µA.

Electrical Measurements & Measuring Instruments Multiple Choice Questions on “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
Clarification: 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
Clarification: 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 = (frac{R_1 R_3}{R_2})
b) R_x = (frac{R_2 R_1}{R_3})
c) R_x = (frac{R_2 R_3}{R_1})
d) R_x = (frac{R_2}{R_1})
Answer: c
Clarification: 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 = (frac{R_2 R_3}{R_1}).

4. The value of unknown inductance is found by using which of the following relation?
a) L_x = (frac{R_1 L_3}{R_2})
b) L_x = (frac{R_2}{R_1})
c) L_x = (frac{L_3}{R_1})
d) L_x = (frac{R_2 L_3}{R_1})
Answer: d
Clarification: At balance condition in an inductance comparison bridge, the value of unknown inductance is found by using the relation L_x = (frac{R_2 L_3}{R_1}).

5. Inductance control is obtained by _________
a) using R₂
b) using R₁
c) using R₃
d) using L_x
Answer: a
Clarification: In an inductance comparison bridge, the resistance R₂ and R₃ are variable. The value of resistance R₂ is varied so as to control the inductance of the bridge.

6. Bridge depends on frequency.
a) True
b) False
Answer: b
Clarification: 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
Clarification: 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
Clarification: 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.

Electrical Measurements & Measuring Instruments Multiple Choice Questions on “Reduction of Errors in Potential Transformers”.

1. Winding resistance of a P.T. can be reduced by _________
a) using thick conductors
b) decreasing the length of the winding
c) shorting the primary and secondary windings
d) using thin conductors
Answer: a
Clarification: In a potential transformer, the winding resistance is usually minimised by using thick conductors and by making use of small length for the turns.

2. Leakage reactance is minimised by _________
a) using thin conductors
b) reducing leakage flux
c) increasing flux density
d) shorting the windings
Answer: b
Clarification: By maintaining the primary and secondary windings together in a P.T. and also by reducing the leakage flux, we can minimise the leakage reactance.

3. High flux density is due to less turns.
a) True
b) False
Answer: a
Clarification: In a P.T., a high flux density in the core, gives rise to a less number of turns. This in turn results in a lower leakage reactance.

4. Ratio error in a P.T. depends on _________
a) secondary current
b) primary voltage
c) secondary current
d) turns ratio
Answer: c
Clarification: In a P.T., the difference between actual ratio and turns ratio is given by the relation,

where, R is the ratio error
n is the turns ratio
I_s is the secondary winding current
I_e is the iron loss component
I_m is the magnetising component
It is seen from the above equation that the ratio error in a P.T. depends on the secondary current, magnetising and iron loss components of current.

5. In a P.T. values of components of currents are negligible.
a) True
b) False
Answer: b
Clarification: In a C.T. the various components of current such as magnetising current, iron loss component of current are almost comparable in magnitude with the value of the load current.

6. Ratio error can be minimised by _________
a) reducing the turns
b) reducing the current
c) increasing the voltage
d) using a good core material
Answer: d
Clarification: By making use of a good quality core material, low value of flux density and following required precautions in the core assembly we can minimise the value of the ratio error.

7. Another method of eliminating the ratio error is _________
a) by reducing secondary turns
b) by increasing the primary turns
c) by increasing secondary turns
d) by reducing the primary turns
Answer: a
Clarification: In a P.T., at no load, we get

where, R is the ratio error
n is the turns ratio
I_s is the secondary winding current
I_e is the iron loss component
I_m is the magnetising component
From the above equation it is seen that to reduce the ratio error, actual ratio and nominal ratio must be made equal. This can be done by reducing the secondary turns.

Electrical Measurements & Measuring Instruments Multiple Choice Questions on “Advantages of Electronic Instruments”.

1. Electronic voltmeters use electronic circuits.
a) True
b) False
Answer: a
Clarification: Voltmeters that make use of rectifiers, diodes, amplifiers, etc in order to produce a current that is in proportion to the quantity that is being measured is known as an electronic voltmeter.

2. In olden days voltmeters were __________
a) made of transistors
b) made of vaccum tubes
c) made of transformers
d) made of diodes
Answer: b
Clarification: Initially, voltmeters were made of vaccum tubes. These voltmeters were known as vaccum tube voltmeters (VTVM).

3. Modern day voltmeters are made of __________
a) made of transformers
b) made of vaccum tubes
c) made of transistors and diodes
d) made of insulated iron coils
Answer: c
Clarification: Nowadays in voltmeters, transistors and semiconductor diodes are used. A transistor voltmeter makes use of transistor in a voltmeter.

4. FETVM is __________
a) an ammeter
b) a galvanometer
c) a multimeter
d) a voltmeter
Answer: d
Clarification: Field effect transistors can also be used at the input. Such voltmeters are known as FETVM (Field Effect Voltmeter).

5. Electronic voltmeters are __________
a) compact
b) large in size
c) not portable
d) difficult to use
Answer: a
Clarification: When compared to conventional analog voltmeters, electronic voltmeters are compact and also portable. This is due to the small size of the components.

6. Electronic voltmeters are not accurate.
a) True
b) False
Answer: b
Clarification: Compared to analog voltmeters, electronic voltmeters are very accurate and precise.

7. Electronic voltmeters are __________
a) dependent of frequency
b) dependent of voltage
c) independent of frequency
d) dependent of current
Answer: c
Clarification: Usually electronic voltmeters can measure frequency in the range of a few volts D.C. to frequencies of the order of hundreds of MHz. As a result, the effect of frequency on the response of electronic voltmeters is negligible.

8. Dynamic range of electronic voltmeter is __________
a) zero
b) limited
c) narrow
d) wide
Answer: d
Clarification: When compared to conventional analog voltmeters, the dynamic range is very wide and improved in electronic voltmeters. Very low as well as very high input signals can be measured using an electronic voltmeter.

9. Loading effect in electronic voltmeters is __________
a) nil
b) high
c) low
d) medium
Answer: a
Clarification: In an electronic voltmeter as the power is supplied by an external circuit, there is no loading effect. In a PMMC instrument, a minimum current of 50 µA is obtained from the signal that is to be measured and this leads to loading effect.

10. Electronic voltmeters are ____________
a) measure high level signals
b) measure low level signals
c) measure medium level signals
d) don’t measure any signal
Answer: b
Clarification: Electronic voltmeters make use of amplifier circuits. As a result they can be used for measuring low level signals.

Electrical Measurements & Measuring Instruments Multiple Choice Questions on “Advanced Problems on Q Meter”.

1. Q meter operator is the principle of __________
a) Series resonance
b) Current resonance
c) Self-inductance
d) Eddy currents
Answer: a
Clarification: We know that Q = (frac{ωL}{R})
From the above relation, we can say that it works on series resonance.

2. In a Q Meter, the values of tuning capacitor are C₃ and C₄ for resonant frequencies f₃ and 2f₄ respectively. The value of distributed capacitance is?
a) (frac{C_3-C_4}{2})
b) (frac{C_3-2C_4}{3})
c) (frac{C_3-4C_4}{3})
d) (frac{C_3-3C_4}{2})
Answer: c
Clarification: Q_X = (frac{R_P}{X_P} = frac{(C_4 – C_3)Q_3 Q_4}{Q_3 C_3 – Q_4 C_4})
The main error in the measurement of Q is due to the distribution. To check for this, the Q value is measured at two frequencies f₁ and 2f₂. It should be same, if not then, (frac{C_3-4C_4}{3}).

3. A circuit tuned to a frequency of 1.5 MHz and having an effective capacitance of 150 pF. In this circuit, the current falls to 70.7 % of its resonant value. The frequency deviates from the resonant frequency by 5 kHz. Q factor is?
a) 50
b) 100
c) 150
d) 200
Answer: c
Clarification: Q = (frac{ω}{ω1 – ω2} = frac{f}{f2-f1})
Here, f = 1.5 × 10⁶ Hz
f1 = (1.5 × 10⁶ – 5 × 10³)
f2 = (1.5 × 10⁶ + 5 × 10³)
So, f2 – f1 = 10 × 10³ Hz
Q = (frac{1.5 × 10^6}{10 × 10^3}) = 150.

4. A circuit tuned to a frequency of 1.5 MHz and having an effective capacitance of 150 pF. In this circuit, the current falls to 70.7 % of its resonant value. The deviates from the resonant frequency are 5 kHz. Effective resistance of the circuit is?
a) 2 Ω
b) 3 Ω
c) 5.5 Ω
d) 4.7 Ω
Answer: d
Clarification: R = (frac{f2-f1}{2πf^2 L})
Here, f = 1.5 × 10⁶ Hz
f1 = (1.5 × 10⁶ – 5 × 10³)
f2 = (1.5 × 10⁶ + 5 × 10³)
So, f2 – f1 = 10 × 10³ Hz
R = (frac{10 × 10^3}{2π(1.5 × 10^6)^2 L})
R = 4.7 Ω.

5. Q Meter is used to measure _________
a) Q factor of an inductive coil
b) Only the effective resistance
c) Only bandwidth
d) Q factor of an inductive coil, the effective resistance, and bandwidth
Answer: d
Clarification: Q meter can measure the Q factor of an inductive coil. It can also measure the effective resistance. Also, the bandwidth can be measured by the Q Meter. Therefore it can be used for all the above functions.

6. Q factor of a coil measured by the Q Meter is _________ the actual Q of the coil.
a) Equal to
b) Same but somewhat lesser than
c) Same but somewhat higher than
d) Not equal to
Answer: b
Clarification: The Q factor measured by the Q meter cannot be exactly equal to the actual Q of the coil because of the presence of errors. Also, it is not practically possible for the value to be higher than the actual one. But the value is somewhat lesser and almost equal to the actual value.

7. Consider a circuit consisting of two capacitors C₁ and C₂. Let R be the resistance and L be the inductance which are connected in series. Let Q₁ and Q₂ be the quality factor for the two capacitors. While measuring the Q value by the Series Connection method, the value of the Q factor is?
a) Q = (frac{(C_1 – C_2 ) Q_1 Q_2}{Q_1 C_1 – Q_2 C_2})
b) Q = ( frac{(C_2 – C_1 ) Q_1 Q_2}{Q_1 C_1 – Q_2 C_2})
c) Q = ( frac{(C_1 – C_2 ) Q_1 Q_2}{Q_2 C_2 – Q_1 C_1})
d) Q = ( frac{(C_2 – C_1 ) C_1 C_2}{Q_1 C_1 – Q_2 C_2})
Answer: a
Clarification: ωL = (frac{1}{ωC})and Q₁ = (frac{ωL}{R} = frac{1}{ωC_1 R})
X_S = (frac{C_1-C_2}{ωC_1 C_2 }), R_S = (frac{Q_1 C_1 – Q_2 C_2}{ωC_1 C_2 Q_1 Q_2})
Q_X = (frac{X_S}{R_S} = frac{(C_1- C_2) Q_1 Q_2}{Q_1 C_1-Q_2 C_2}).

8. Consider a circuit consisting of two capacitors C₁ and C₂. Let R be the resistance and L be the inductance which are connected in series. Let Q₁ and Q₂ be the quality factor for the two capacitors. While measuring the Q value by the Parallel Connection method, the value of the Q factor is?
a) Q = (frac{(C_1 – C_2 ) Q_1 Q_2}{Q_1 C_1 – Q_2 C_2})
b) Q = (frac{(C_2 – C_1 ) Q_1 Q_2}{Q_1 C_1 – Q_2 C_2})
c) Q = (frac{(C_1 – C_2 ) Q_1 Q_2}{Q_2 C_2 – Q_1 C_1})
d) Q = (frac{(C_2 – C_1 ) C_1 C_2}{Q_1 C_1 – Q_2 C_2})
Answer: b
Clarification: (frac{1}{R_P} = frac{ωC_1}{Q_2} – frac{1}{RQ_1^2}), X_P = (frac{1}{ω(C_2 – C_1)})
Q = (frac{(C_2 – C_1 ) Q_1 Q_2}{Q_1 C_1 – Q_2 C_2}).

9. Consider the following statements regarding the sources of error in a Q Meter.

i) If a coil with a resistance R is connected in the direct measurement mode and
If the residual resistance of the Q Meter is 0.1 R, 
Then the measured Q of the coil would be 1.1 times the actual Q.
ii) If the inductance to be measured is less than 0.1 μH.
The error due to the presence of residual inductance cannot be neglected.
iii) The presence of a distributed capacitance modifies the effective Q of the coil.

Which of the above statements are correct?
a) i, ii and iii
b) i and ii
c) ii and iii
d) i and iii
Answer: c
Clarification: We know that, Q = (frac{Lω}{R})
With Q Meter resistance considered, the measured or indicated Q is 1/1.11 times the actual Q. Thus, statement (i) is incorrect. Hence, statements (ii) and (iii) are correct.

10. The function of the Q- Meter is to _________
a) Measure capacitance
b) Measure inductance
c) Measure quality factor of capacitor and inductor
d) Measure form factor of capacitor and inductor
Answer: c
Clarification: Q-Meters are intended to measure the quality factor of a capacitor and inductor. Q = (frac{Lω}{R} = frac{1}{ωCR} = frac{V_C}{V_A}). They are not used for measuring capacitances and inductances, unlike AC Bridges.

Category: Electrical Measurements Objective Questions

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