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Multiple choice question for engineering

Set 1

1. Front panel of a CRO has _________
a) 4 sections
b) 8 sections
c) 15 sections
d) 20 sections

View Answer

Answer: a [Reason:] A simple Cathode Ray Oscilloscope has the following four sections: i) Basic controls ii) Vertical section iii) Horizontal section iv) Z axis intensity control.

2. What is the role of intensity section in a CRO?
a) decreases the light intensity
b) controls light intensity
c) increases the light intensity
d) keeps the light intensity zero

View Answer

Answer: b [Reason:] In a Cathode Ray Oscilloscope the intensity section controls the brightness or intensity of the light beam produced by the bombardment of electrons on the fluorescent screen.

3. What is the role of the focus section in a CRO?
a) increases the focus
b) decreases the focus
c) controls sharpness
d) maintains the focus zero

View Answer

Answer: c [Reason:] In a Cathode Ray Oscilloscope the focus section controls the sharpness of the visible spot on the screen. By varying the voltage applied to the focussing anodes, visible spot on the screen is focussed sharply.

4. What is the role of astigmatism in a CRO?
a) increases the intensity
b) used for voltage stability
c) diminishes the intensity
d) focus control

View Answer

Answer: d [Reason:] In a Cathode Ray Oscilloscope the astigmatism forms another set of focus control. A sharp spot can be obtained by the combination of focus control and astigmatism.

5. What is the role of scale illumination in a CRO?
a) measurement
b) illumination
c) sharpness
d) stability

View Answer

Answer: a [Reason:] In a Cathode Ray Oscilloscope the scale illumination is basically used for the purpose of measurement. It basically illuminates the scale and as a result the reading can be clearly seen.

6. What is the role of an invert in a CRO?
a) inverts the output
b) inverts the input
c) attenuates the input
d) magnifies the input

View Answer

Answer: b [Reason:] In a Cathode Ray Oscilloscope the invert control section is used for the purpose of inverting the input signal. It basically multiplies the input signal by a factor of -1.

7. X10 in a CRO means ________
a) one tenth
b) control knob
c) 10 times as normal
d) attenuate the voltage by 10 times

View Answer

Answer: c [Reason:] In a Cathode Ray Oscilloscope X10 indicates that gain of the vertical amplifier is made 10 times that of the normal value. When the X10 switch is turned ON, scope of the CRO is et to 0.05 V/cm.

8. Position knob in a CRO indicates ________
a) voltage position only
b) time position only
c) current position only
d) any pattern’s position

View Answer

Answer: d [Reason:] In a Cathode Ray Oscilloscope the position knob is used for indicating the position of any pattern on the screen. The pattern can be shifted vertically upwards or downwards.

9. Alternate is used to shift the inputs.
a) True
b) False

View Answer

Answer: a [Reason:] In a Cathode Ray Oscilloscope the alternate knob is used to transition between the two different input signals. Using the vertical position control, the traces of the two input signals are separated vertically.

Set 2

1. Mutual inductance between two coils is given as
electrical-measurements-questions-answers-inductive-transducer-q1

View Answer

Answer: a [Reason:] The mutual inductance between two coils is given by the relation electrical-measurements-questions-answers-inductive-transducer-q1a where, k is the coefficient of coupling M is the mutual inductance between the coils.

2. Mutual inductance depends on _________
a) self-inductance
b) self-inductance and coefficient of coupling
c) coefficient of coupling
d) permittivity of air

View Answer

Answer: b [Reason:] The mutual inductance of a pair of coils depends on the self-inductance of the individual coils and on the coefficient of coupling.

3. Self-inductance of an inductor is given by ________
a) L = NS
b) L = 1S
c) L = N2S
d) L = N2

View Answer

Answer: c [Reason:] The self-inductance of an inductor is obtained by making use of the relation L = N2S where, N is the number of coil S is the reluctance of the coil (A/Wb).

4. Reluctance of a coil is given by the relation
a) S = 1A
b) S = 1μ
c) S = aμA
d) S = 1μA

View Answer

Answer: d [Reason:] The reluctance of an inductance coil is given by the relation S = 1μA where, l is the length of the magnetic circuit (m) a is the area of the magnetic circuit which encloses the flux (m2) µ is the permeability of the core (H/m).

5. Self-inductance depends on ________
a) permeability
b) permittivity
c) plank’s constant
d) rydberg constant

View Answer

Answer: a [Reason:] The self-inductance of an inductor is obtained by making use of the relation L = N2S where, N is the number of coil S is the reluctance of the coil (A/Wb) As reluctance depends on the permeability, the self-inductance of a coil depends on the permeability.

6. What is the relation between the self-inductance and the reluctance of a coil?
a) directly proportional
b) inversely proportional
c) no relation
d) constant

View Answer

Answer: b [Reason:] The self-inductance of an inductor is obtained by making use of the relation L = N2S where, N is the number of coil S is the reluctance of the coil (A/Wb) We observe from the above equation that the self-inductance of a coil is inversely proportional to its reluctance.

7. Based on self-inductance of a coil, how many types of inductive transducers are available?
a) 5
b) 10
c) 4
d) 20

View Answer

Answer: c [Reason:] Based on the self-inductance of an inductive coil, there are four types of inductive transducers available. They are as follows: Variable permeability inductive transducer Variable reluctance inductive transducer Eddy current inductive transducer Linear variable differential transducer.

8. In an eddy current transducer output depends on the variation in the eddy current.
a) True
b) False

View Answer

Answer: a [Reason:] An eddy current transducer is a self-generating type of inductive transducer. In an eddy current transducer, output depends on the change in the value of the eddy current at the input.

9. An inductive transducer measures the variation in ________
a) reluctance
b) resistance
c) capacitance
d) self-inductance

View Answer

Answer: d [Reason:] Inductive transducer measures the variation in the self-inductance and mutual inductance of an inductive coil. Variation in the inductance is measured as a change in the displacement.

10. Inductive transducer is used for measurement of physical quantities.
a) True
b) False

View Answer

Answer: a [Reason:] An inductive transducer is usually used for the measurement of physical quantities such as pressure, force, displacement, position, vibration, velocity, etc.

Set 3

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

View Answer

Answer: a [Reason:] 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

View Answer

Answer: b [Reason:] 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

View Answer

Answer: c [Reason:] 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

View Answer

Answer: a [Reason:] 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

View Answer

Answer: d [Reason:] 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

View Answer

Answer: a [Reason:] 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

View Answer

Answer: b [Reason:] 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

View Answer

Answer: c [Reason:] 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

View Answer

Answer: d [Reason:] 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.

Set 4

1. The energy meter always measures the load energy correctly.
a) True
b) False

View Answer

Answer: b [Reason:] When the difference in phase angles between the shunt magnetic flux and the applied voltage is 90 degrees (lagging), the reading of the load energy obtained from an energy meter is correct.

2. Obtaining correct reading from the energy meter requires
a) low resistance and iron losses
b) high resistance and iron losses
c) high resistance and low iron losses
d) low resistance and high iron losses

View Answer

Answer: a [Reason:] In order to obtain exact reading for the energy consumed by a load using an energy meter, we require the pressure coil to have a low value of resistance and low iron losses.

3. Phase angle can be made 90 degrees using
a) lead circuit
b) lag circuit
c) special design
d) transformer

View Answer

Answer: c [Reason:] Phase angle in an energy meter can be made approximately 90 degrees by making use of a special design in the energy meter.

4. Shading coil consists of many thick turns.
a) True
b) False

View Answer

Answer: b [Reason:] On the central limb of a shunt magnet we can make use of a shading coil. The shading coil consists of a few fairly thick turns. Figure below shows a shading coil on the central limb of the shunt magnet. electrical-measurements-questions-answers-lag-adjustment-devices-q4

5. Copper shading bands are _________
a) placed as resistance
b) placed as wire
c) placed outside the central limb
d) placed around central limb

View Answer

Answer: d [Reason:] The central limb of a shunt magnet consists of copper shading bands. They can be moved up or down by making use of the central limb. Figure below illustrates the use of copper shading bands. electrical-measurements-questions-answers-lag-adjustment-devices-q5

6. As copper shading bands move up
a) more flux is induced
b) less flux is induced
c) intermediate flux is induced
d) no flux is induced

View Answer

Answer: a [Reason:] When the copper shading bands are moved up the central limb, more flux is induced. As a result the difference in angle between the phase and voltage increases. The angle can be made approximately equal to 90 degrees.

7. Shunt flux is made to lag the applied voltage using
a) lead circuit
b) lag adjustment
c) lead-lag circuit
d) transformer

View Answer

Answer: b [Reason:] We make use of shading coil on the central limb of a shunt magnet and shading bands in order to make the shunt flux to lag the applied voltage by almost 90 degrees.

8. At overloads, magnetic shunt ________
a) aids the series flux
b) diverts series flux
c) maintains zero flux
d) disables the shunt flux

View Answer

Answer: b [Reason:] As the magnetic shunt reaches saturation at overloads, magnetic shunt diverts the flux due to series magnet. As a result a large portion of the flux appears in the gap of the air disc. This compensates the self braking torque.

Set 5

1. Wheatstone bridge can’t be used for measurement of
a) high resistance
b) medium resistance
c) low resistance
d) accurate resistance

View Answer

Answer: a [Reason:] Wheatstone bridge can be used for the measurement of medium resistances only. Kelvin bridge is used for the measurement of medium resistances.

2. Cost of maintenance of Wheatstone bridge is _________
a) low
b) high
c) depends on the components
d) depends on the source e.m.f

View Answer

Answer: b [Reason:] As the resistance must have a tolerance of upto 1%, cost of maintenance of the Wheatstone bridge circuit is expensive. Voltage source does not add to the cost of maintenance of a Wheatstone bridge as it is uniform for all bridge circuits.

3. What is the effect of galvanometer on measurement of high resistance?
a) no effect
b) depends on the e.m.f source
c) galvanometer becomes insensitive to imbalance
d) depends on the type of galvanometer used

View Answer

Answer: c [Reason:] If the Wheatstone bridge is used for the measurement of high resistance, the galvanometer becomes insensitive and does not detect any imbalance.

4. What is the effect of heat on the resistances in a Wheatstone bridge?
a) no effect
b) increases the voltage drop across the circuit
c) decreases the current flowing through the circuit
d) causes a permanent change in the resistance values

View Answer

Answer: d [Reason:] As the current flowing through the Wheatstone bridge circuit increases, the temperature of the resistance increases. As a result the resistance values are changed permanently.

5. Effect of high dc on Wheatstone bridge.
a) no effect
b) not susceptible
c) burns the circuit
d) increases the temperature

View Answer

Answer: b [Reason:] A Wheatstone bridge is not susceptible to the flow of high dc current. A Wheatstone bridge in simplest form is used for the measurement of resistance with values in the medium resistance range.

6. A Wheatstone bridge may not give accurate readings if _________
a) it is not balanced
b) it is balanced
c) the voltage drop across the circuit is maximum
d) excessive current flows through the circuit

View Answer

Answer: a [Reason:] A Wheatstone bridge circuit may give inaccurate measurement of resistance if it is not balanced properly. Current flow through a Wheatstone bridge circuit is fixed as the e.m.f source magnitude is constant.

7. What is the effect of lead wires on the Wheatstone bridge?
a) no effect
b) stabilizes the system
c) desensitizes the system
d) increases the resistance of the circuit

View Answer

Answer: c [Reason:] The lead wires connecting the resistance arms of a Wheatstone bridge add to the existing values of resistances across the ratio arms. As a result the net value of resistance changes, thus destabilizing the system.

8. Why a Wheatstone bridge can’t be used for signal conditioning?
a) due to the galvanometer
b) due to excessive current flow
c) due to the e.m.f source used
d) due to lead wires

View Answer

Answer: d [Reason:] Lead wires add to the resistance of the arms of the Wheatstone bridge. As a result the bridge circuit is destabilized and can’t be be used for signal conditioning.

9. How to minimize the drift in the value of resistance measured using a Wheatstone bridge?
a) by using a high precision null detector
b) by keeping the lead wire resistances within 0.2 mΩ
c) by using a e.m.f source of minimum value
d) by minimizing the flow of current

View Answer

Answer: b [Reason:] The drift in the measured value of resistance in a Wheatstone bridge can be minimized by maintaining the lead wire resistances within 0.2 mΩ. As a result the effect of lead wire resistance gets removed in the output value of the bridge circuit.

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