Multiple choice question for engineering
1. In a voltage to frequency converter type integrated DVM,
a) voltage is converted to time
b) voltage is converted to frequency
c) frequency is converted to voltage
d) frequency is converted to time
Answer: a [Reason:] We know that the quantities time and frequency are related to each other. Voltage is converted into time in a voltage to frequency converter type integrating DVM.
2. Input voltage is measured by
a) using a voltmeter
b) counting pulses
c) using a multimeter
d) using an ammeter
Answer: b [Reason:] A pulse train is generated. Their frequency depends on the frequency of the unknown voltage. Number of pulses present in a definite interval are counted. Unknown input voltage is a measure of the pulses generated.
3. Main component of an integrating type DVM is
c) op amp
Answer: c [Reason:] An op amp forms the heart of the integrating type DVM. Op amp is used as an integrator. The input signal is integrated for a fixed interval giving rise to a ramp signal at the output.
4. When input is positive, the output is
a) growing exponential signal
b) decaying exponential signal
c) positive going ramp
d) negative going ramp
Answer: d [Reason:] The op amp produces a negative going ramp signal for a positive input voltage. Capacitor is discharged after some time and the output returns to zero. The next cycle starts and the output is a sawtooth waveform. Figure shows the output sawtooth waveform.
5. What is the effect of the input signal on the output teeth?
a) directly proportional
b) inversely proportional
d) square proportional
Answer: a [Reason:] When the input signal in a voltage to frequency conversion type integrated DVM is doubled, the number of tooth in the output signal is doubled per unit time. This doubles the frequency of the output signal.
6. Sawtooth pulses enter into a reversible counter.
Answer: a [Reason:] The sawtooth output signal obtained from the integrating type DVM is passed through a reversible counter. A digital readout displays the value measured by the reversible counter.
7. Application of an input voltage generates a
a) linear signal at the output
b) ramp at the output
c) exponential signal at the output
d) unit step signal at the output
Answer: b [Reason:] When an input voltage of magnitude Vin is applied at the input, capacitor C is charged by the charging current Vin/R1. As a result a ramp signal is produced at the output.
8. Number of pulses is related to frequency.
Answer: a [Reason:] Each tooth in the sawtooth waveform produces a pulse at the output of the pulse generator. Hence the number of tooth i.e. the frequency is directly related to the number of pulses.
9. Accuracy depends on
a) input voltage
b) drop across the capacitor
c) magnitude and stability of pulse generator
d) magnitude of the ramp
Answer: c [Reason:] Accuracy of the voltage to frequency conversion depends on the capacity of the pulse generator to produce electric charge with a suitable magnitude and stability. Hence the accuracy depends on the precision of the charge feedback.
1. Electrical strain gauge works on the principle of __________
a) variation of resistance
b) variation of capacitance
c) variation of inductance
d) variation of area
Answer: a [Reason:] An electrical strain gauge works on the basis of change in resistance as a function of strain. The wire resistance increases with tension and reduces with compression.
2. The strain gauge is not bonded to the specimen.
Answer: b [Reason:] The gauge is under the same strain as that the specimen under test. As a result the strain gauge is bonded to the specimen.
3. Bonding element in a strain gauge must have __________
a) zero insulation resistance
b) low insulation resistance
c) high insulation resistance
d) infinite insulation resistance
Answer: c [Reason:] In a strain gauge, the bonding element must have a high value of insulation resistance. It should be immune to effects of moisture and must also have the ability to transmit strain.
4. Dynamic strain measurements use __________
a) brass iron alloy
b) iron aluminium alloy
c) nickel cadmium alloy
d) nickel chromium alloy
Answer: d [Reason:] Nickel chromium alloy is also known as a nichrome alloy. It contains 80 % of Nickel and 20 % of Chromium. Platinum is used for the temperature compensation of nickel chromium alloys.
5. Commonly used elements for wire strain gauges are __________
a) nickel and copper
b) nickel and gold
c) gold and brass
d) silver and aluminium
Answer: a [Reason:] Nickel and copper are the most commonly used elements for wire strain gauges. They comprise of 45 % of Nickel and 55 % of Copper. They exhibit a high value of specific resistance.
6. Cement is classified under __________
a) 4 types
b) 2 types
c) 6 types
d) 8 types
Answer: b [Reason:] Cement can be divided into two broad categories. They are as follows:
Solvent setting cement
Chemically reacting cement.
7. Proper functioning of a strain gauge depends on __________
d) length of wire
Answer: c [Reason:] A strain gauge works properly only if the bonding material used is durable and keeps the gauge together to the surface of the material that is being tested.
8. Gauge factor is given by the relation __________
Answer: d [Reason:] Gauge factor in a strain gauge is given by the relation
where, S is the gauge factor
R is the gauge wire resistance
∆R is the change in resistance
l is the length of the wire in unstressed condition
∆l is the change in length of the wire.
9. Poisson’s ratio is given by ____________
Answer: a [Reason:] Poisson’s ratio is given by the relation
where, d is the diameter of the cross-section of the wire
∆d is the change in the diameter of cross-section of the wire.
10. Proper bonding causes errors in strain gauges.
Answer: b [Reason:] Strain gauge is fixed onto the specimen by means of a bonding element. Cement is the commonly used adhesive. It transfers the strain from the specimen to the gauge sensing element.
1. CRO stands for __________
a) Cathode Ray Oscilloscope
b) Current Resistance Oscillator
c) Central Resistance Oscillator
d) Capacitance Resistance Oscilloscope
Answer: a [Reason:] Cathode Ray Oscilloscope (C.R.O) is basically used for the measurement of the amplitude of periodic and non periodic signals as a function of time.
2. C.R.O gives __________
a) actual representation
b) visual representation
c) approximate representation
d) incorrect representation
Answer: b [Reason:] Cathode Ray Oscilloscope is used as universal laboratory equipment. It provides a visual representation of time varying signals. It is an important equipment in the development of electronic circuits.
3. Oscilloscope is __________
a) a ohmmeter
b) an ammeter
c) a voltmeter
d) a multimeter
Answer: c [Reason:] Oscilloscope is basically a voltmeter. It employs the movement of an electronic gun assembly with respect to a fluorescent screen. The screen produces the movement of the visible spot.
4. Electron beam is deflected in __________
a) 1 direction
b) 4 directions
c) 3 directions
d) 2 directions
Answer: d [Reason:] The electron beam in an oscilloscope can be deflected in two directions, namely the horizontal (x-direction) and the vertical (y-direction). Two dimensional displays are produced as a result.
5. CRO is a __________
a) fast x-y plotter
b) slow x-y plotter
c) medium x-y plotter
d) not a plotter
Answer: a [Reason:] CRO is basically a fast x-y plotter. The x and y axes can be used to understand the variation in the magnitude of one voltage with respect to another voltage signal.
6. CRO can’t display microseconds time.
Answer: b [Reason:] CRO is a fast x-y plotter and displays periodic signals with time periods of the order of a few microseconds and even nanoseconds.
7. CRT is the heart of CRO.
Answer: a [Reason:] CRT stands for Cathode Ray Tube. It generates electron beam, accelerates and deflects the beam. It thus forms the heart of the CRO.
8. Typically oscilloscope represents __________
a) current and time
b) resistance and time
c) voltage and time
d) power and time
Answer: c [Reason:] In an oscilloscope typically the horizontal or x-axis represents the time while the vertical or y-axis represents the variation in the magnitude of the input signal.
1. Basic range of DVM is _________
a) 1 or 10 V
b) 0.1 or 1 V
c) 10 or 100 V
d) 100 or 1000 V
Answer: a [Reason:] In a DVM, the basic range is 1 V or 10 V. Range of a DVM can be extended from a few µV to kV. This is achieved by making use of an attenuator.
2. Accuracy of a DVM is ________
Answer: b [Reason:] Accuracy of a DVM is based on the resolution. Resolution depends on the number of digits. The more the number of digits, the higher is the accuracy. For a DVM, the accuracy is of the order of ±0.005 % of the reading.
3. Input impedance of a DVM is ________
Answer: c [Reason:] Typical input impedance of a DVM is usually very high. Typical value is of the order of 10 MΩ. This is usually done in order to reduce the loading effect.
4. In DVM the common mode rejection noise is eliminated by ________
a) increasing the signal amplitude
b) making use of a resistance
c) using a transformer
Answer: d [Reason:] In a DVM, common mode noise can be eliminated through guarding. A guard is basically a sheet metal box around the circuit. This is made available to the circuit being measured by making use of a terminal at the front panel.
5. Output of DVM needs ________
a) 4 lines
b) 2 lines
c) 8 lines
d) 16 lines
Answer: a [Reason:] Type of DVM used depends on the digital output lines. Four lines of BCD or a single line serial output may be provided so as to read the output from a DVM.
6. Normal mode noise can be eliminated through ________
d) a transformer
Answer: b [Reason:] Filters can be used to eliminate the normal mode noise signals. When used for low voltage measurement, noise present at the input can cause errors in the analog to digital converter.
7. DVM has ________
a) 1-3 digits
b) 2-5 digits
c) 3-6 digits
d) 7-10 digits
Answer: c [Reason:] The DVM consists of 3 to 6 digits. As the number of digits are increased the resolution also increases. Thus, the resolution of a DVM is very high.
8. What is a digitizing circuit?
a) converts digital signal to analog
b) boosts the magnitude of a digital signal
c) attenuates a digital signal
d) converts analog signal to digital
Answer: d [Reason:] DVM converts analog signal to digital. The process is known as digitization and the circuit used to obtain the conversion is known as a digitizing circuit. Time needed for this conversion is known as digitizing period.
9. User must wait for a stable reading.
Answer: a [Reason:] Since it is difficult to follow the reading visually at high reading speeds, user has to wait till a stable reading is obtained. Digitizing period depends on the maximum speed at which the value is read from the meter.
1. Phase sequence indicator gives the maximum value of phase voltages.
Answer: a [Reason:] The phase sequence for a three phase supply indicates the order in which maximum values of phase voltages ER, EY, and EB occur. A three phase supply can be in either RYB or RBY configuration.
2. Synchronization of A.C. supply means __________
a) different phase sequence
b) same phase sequence
c) zero phase
d) using a transformer
Answer: b [Reason:] During synchronization, the phase sequences of any two given supplies are maintained equal. This is ensured by making use of a phase sequence indicator.
3. How many types of phase sequence indicators are there?
Answer: c [Reason:] Generally, two types of phase sequence indicators are used. The first one is the rotating type while the second type is the static type. Usually the rotating type of phase sequence indicator is used.
4. A rotating phase sequence indicator consists of ________
a) 1 coil
b) 2 coils
c) 5 coils
d) 3 coils
Answer: d [Reason:] A rotating type of phase sequence indicator basically consists of three coils. These are mounted at 120º to each other is space. The ends of the coils are connected to the terminals R, Y, and B respectively.
5. The three coils are ________
a) star connected
b) delta connected
c) not connected
Answer: a [Reason:] In a rotating type phase sequence indicator, the three coils are connected in the form of a star and excited by a three-phase supply.
6. Excitation of the three coils produces ________
a) a static magnetic field
b) a rotating magnetic field
c) a static electric field
d) a rotating electric field
Answer: b [Reason:] Aluminum disc is mounted on the top of the three coils. A rotating magnetic field is produced when the three coils are excited by a supply of three phase. As a result e.m.f with eddy current effects are induced in the coils.
7. Eddy e.m.f produces a torque.
Answer: a [Reason:] A rotating magnetic field is produced when the three coils are excited by a supply of three phase. As a result, eddy e.m.f circulate in the disc. A torque is produced as a result of the interaction between the eddy currents and the rotating magnetic field.
8. Disc rotation is determined by ________
a) the supply voltage
b) an arrow
c) the turns ratio
d) the load current
Answer: b [Reason:] Direction of rotation of the disc is determined by making use of an arrow that is marked on the disc. The phase sequence of the supply voltage is same as that mentioned on the terminals of the meter provided disc rotates in the same direction as the arrow head.