Category: Electrical Measurements Objective Questions

Electrical Measurements Questions and Answers for Campus interviews on “Advantages and Limitations of Maxwell Bridge”.

1. What is the significance of the balance equation on losses?
a) independent of losses in inductance
b) independent of losses in capacitance
c) independent of losses in resistance
d) independent of losses in the circuit
Answer: a
Clarification: The balance equation in a Maxwell inductance capacitance bridge is independent of the losses associated with an inductance. According to the balance equation the unknown inductance is computed as L_x = R₂ R₃ C₁.

2. Balance equation is dependent on frequency.
a) True
b) False
Answer: b
Clarification: The balance equation in a Maxwell inductance capacitance bridge is independent on the measurement of frequency. The balance equation does not contain frequency terms such as ω and as a result, it is independent of frequency.

3. How can R₁ be scaled?
a) by using a scale
b) by using an ohmmeter
c) by calibration
d) by using a galvanometer
Answer: c
Clarification: The resistance R₁ in a Maxwell inductance capacitance bridge can be scaled through calibration. The value of the Quality factor Q can be read directly through calibration.

4. Scale of resistance can be calibrated.
a) True
b) False
Answer: a
Clarification: The resistance R₁ in a Maxwell inductance capacitance bridge can be calibrated directly. As a result the value of the unknown inductance can be read directly.

5. Bridge can be used for the measurement of _________
a) high Q values
b) intermediate Q values
c) very low Q values
d) low Q values
Answer: d
Clarification: A Maxwell inductance capacitance bridge can be used for the measurement of low Q values only of the order of 1 to 10. This is because at high Q factor values the angular balance condition is not satisfied.

6. The balance condition is _________
a) is easy to obtain
b) is difficult to obtain
c) can’t be obtained
d) exists always
Answer: b
Clarification: The balance condition in a Maxwell inductance capacitance bridge is difficult to obtain. This occurs due to an interaction between resistance and reactance components in the bridge circuit.

7. Commercial Maxwell bridges measures _________
a) inductances in the range of 1 to 1000H
b) capacitances in the range of 10mF to 1F
c) resistances in the range of 0.001 Ω to 1Ω
d) power in the range of 1W to 50MF
Answer: a
Clarification: Basically a Maxwell bridge is used for the measurement of inductance in terms of known standard capacitance value. Inductances in the range of 1 to 1000H with an accuracy range of ±2% can be measured.

8. At high Q values, the angular balance condition is _________
a) satisfied
b) not satisfied
c) independent of Q factor
d) partially affected
Answer: b
Clarification: For high Q factor values in a Maxwell inductance capacitance bridge, the angular balance condition is affected. The relation θ₁ + θ₄ = θ₂ + θ₃ is not satisfied at high Q factor values. This occurs as θ₄ reaches 90°. θ₁ must become –90° as per the angular balance condition. But for this the value of R₁ should be very high, which is not practically feasible.

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Electrical Measurements & Measuring Instruments Multiple Choice Questions on “Dynamometer Type Wattmeter”.

1. Power is ___________
a) rate of doing work
b) rate of producing voltage
c) rate of generating current
d) rate of overcoming friction
Answer: a
Clarification: Power is defined as the rate of doing work. The unit of power is watt. In D.C. circuits, power is the product of the voltage consumed and the current flowing through a circuit. P = VI watts.

2. In A.C. circuits, power consumed is ________
a) product of voltage and current
b) it depends on the p.f. of the circuit in addition to voltage and current
c) it depends on the supply voltage
d) it depends on the magnitude of the circuit current
Answer: b
Clarification: In a A.C. circuit, the power consumption is given by the expression,
P = VI cos∅
where, V is the voltage across the circuit
I is the current flowing through the circuit
cos∅ is the power factor of the circuit.

3. In D.C. circuits, power is measured using ________
a) ohmmeter and galvanometer
b) ohmmeter and voltmeter
c) ammeter and voltmeter
d) ammeter and galvanometer
Answer: c
Clarification: An ammeter is used to measure current flowing through a circuit, while a voltmeter is used to measure the voltage across the circuit. Hence in D.C. circuits, ammeter and voltmeter are used to measure power.

4. In A.C. circuits, power is measured using ________
a) voltmeter
b) ammeter
c) ohmmeter
d) wattmeter
Answer: d
Clarification: A.C. circuits make use of power factor of the circuit in addition to the current flowing through the circuit and the voltage across the circuit. As a result, a wattmeter is used to measure A.C. power.

5. A wattmeter consists of a current coil and a potential coil.
a) True
b) False
Answer: a
Clarification: Power in single phase A.C. circuits are measured by making use of a wattmeter. It consists of a current coil (cc) and a potential coil (pc). Current coil is connected with the load while the potential coil is connected across the supply.

6. A dynamometer type wattmeter consists of ________
a) only potential coil
b) potential and current coils
c) only current coil
d) no coils
Answer: b
Clarification: Dynamometer type wattmeter is used for the measurement of A.C. as well as D.C. power. It consists of a fixed coil forming the current coil whereas the moving coil forms the potential coil.

7. Controlling torque is provided by gold springs.
a) True
b) False
Answer: b
Clarification: In a Dynamometer type wattmeter, controlling torque is provided by two phosphor bronze hair springs. They act as leads to the current flowing through the coil. Also air friction damping is used.

8. In a Dynamometer type wattmeter, the fixed coil is split into ________
a) 4
b) 3
c) 2
d) 1
Answer: c
Clarification: When a Dynamometer type wattmeter is used for the measurement of A.C. power, the fixed coil is split into two equal parts. The two parts are air-cored to avoid hysteresis loss.

9. When a current carrying coil is placed in the magnetic field?
a) no force is exerted
b) voltage is produced
c) power is generated
d) a force is exerted
Answer: d
Clarification: When the current carrying coil of a Dynamometer type wattmeter is placed in the magnetic field of another current carrying coil, the moving coil experiences a force. As a result a deflection torque is generated and the moving coil undergoes deflection.

10. When the moving coil in a Dynamometer type wattmeter deflects ________
a) pointer moves
b) pointer doesn’t move
c) current flows
d) voltage is generated
Answer: a
Clarification: In a Dynamometer type wattmeter, when the moving coil deflects the pointer moves over the scale. The pointer then comes back to rest at a point where the deflecting torque equals the controlling torque.

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

1. Digital voltmeters converts ________
a) analog to digital signal
b) digital to analog signal
c) current to voltage
d) resistance to voltage
Answer: a
Clarification: In general digital voltmeters are known as DVM. They convert analog signals into digital voltage. They also display the voltage to be measured in the form of discrete numerals in place of pointer deflection.

2. Digital voltmeters can be used to measure ________
a) voltage only
b) voltage, temperature, pressure, etc
c) voltage and current
d) voltage and resistance
Answer: b
Clarification: Digital voltmeters are used for the measurement of A.C. as well as D.C. voltages and also to measure physical quantities such as temperature, pressure, stress etc. through the use of appropriate transducer and signal conditioning circuits.

3. A digital voltmeter reduces parallax error.
a) True
b) False
Answer: a
Clarification: A digital voltmeter minimizes the errors due to human interference, interpolation mismatch and errors due to parallax. A digital display is used to show the output voltage on a front panel.

4. In a DVM, a transducer converts ________
a) input to a proportional current
b) input to a proportional power
c) input to a proportional voltage
d) input to a proportional resistance
Answer: c
Clarification: In a digital voltmeter, a transducer is used. In general a transducer converts a physical quantity into an electrical signal. In a DVM the transducer converts the input signal into a proportional voltage.

5. In a DVM, a signal conditioning circuit is used ________
a) to bring current to a suitable limit
b) to bring resistance to a suitable limit
c) to bring resistance to s suitable limit
d) to bring voltage to a suitable limit
Answer: d
Clarification: In a DVM, signal conditioning circuit is used. It converts the input signal into an voltage of suitable limit. This is done so that the voltmeter can read the magnitude of the signal correctly.

6. Input range of DVM is _________
a) 1 V to 1000 V
b) 0.1 V to 10 V
c) 0.01 V to 1 V
d) 0.001 V to 0.1 V
Answer: a
Clarification: In a DVM, the input voltage range is given as 1 V to 1000 V. It includes automatic range selection and overload indication.

7. Output in digital form can’t be used directly.
a) True
b) False
Answer: b
Clarification: The output obtained from a DVM can be used directly. It can be recorded and is also suitable for further processing.

8. What is the effect of IC chips on DVM?
a) increase in cost
b) increase in power
c) reduction in cost
d) increase in size
Answer: c
Clarification: Advancement in IC chips have ensured the reduction in the cost of the DVM’s. Size and power needs of DVM’s have been reduced by a huge margin.

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Electrical Measurements & Measuring Instruments Multiple Choice Questions on “Shielding and Grounding of Bridges”.

1. In general bridges consist of __________
a) lumped inductances
b) lumped resistances
c) distributed capacitance
d) distributed impedance
Answer: a
Clarification: AC bridges in general such as Maxwell, Anderson, Schering, etc consist of lumped components such as inductance.

2. Stray capacitance exists between the components.
a) True
b) False
Answer: a
Clarification: In general in AC bridges, stray capacitance exists between the components of the bridge with respect to the ground. These stray capacitances short the ratio arms and lead to errors in the measurement.

3. The magnitude of stray capacitances is fixed.
a) True
b) False
Answer: b
Clarification: Stray capacitances are uncertain in nature. Their magnitude depends on the adjustment of the bridge arms and the position of the operator.

4. Stray capacitance effects can be minimized by __________
a) making use of an inductance
b) connecting a resistance in series
c) shielding and grounding
d) using a galvanometer
Answer: c
Clarification: The stray capacitance effects in an AC bridge can be eliminated by shielding and grounding. This method helps in making the stray capacitances constant in value. They can be compensated.

5. Most popular method of avoiding the stray capacitance effects is __________
a) by grounding
b) by using guard rings
c) by using galvanometer
d) by using Wagner device
Answer: d
Clarification: A Wagner earthing device is used in general to eliminate the stray capacitance effects in AC bridges. The stray capacitance effects between the components in the ratio arms with respect to ground can be eliminated through this method.

6. Wagner device is a ____________
a) capacitance bridge
b) resistance bridge
c) inductance bridge
d) impedance bridge
Answer: a
Clarification: A Wagner earth device is generally used for shielding and grounding purpose. It consists of capacitances in the ratio arms along with a series RC combination connected across the ends of the bridge forming a potential divider.

7. Which is the guarding arm?
a) parallel RC combination
b) series RC combination
c) resistance R
d) capacitance C
Answer: b
Clarification: The series combination of R and C in a Wagner earth device forms a potential divider across the ratio arms. It is also known as the guard arm.

8. Bridge is suitable for _________
a) coils with high Q values
b) coils with low Q values
c) coils with intermediate Q values
d) coils with very high Q values
Answer: b
Clarification: The Maxwell inductance capacitance bridge is basically used for the measurement of quality factor (Q) of inductance coils with low Q values.

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