Quiz: Electrical Engineering 17 Apr 2021

Quiz: Electrical Engineering
Exam: DSSSB-JE
Topic: Measurement and measuring instrument

Each question carries 1 mark.
Negative marking: 1/4 mark
Time: 10 Minute

Q1. The multiplier and the meter coil in a voltmeter are connected in:
(a) Parallel
(b) Series
(c) Series-parallel
(d) No connection

Q2. The RMS value of a complex waveforms are measured using –
(a) Voltmeter containing heat sensing elements such as thermocouples
(b) High voltmeters
(c) differential voltmeter
(d) Transistor Voltmeter

Q3. What does the CRT oscilloscope display?
(a) Voltage and period
(b) Current and frequency
(c) RMS voltage and current
(d) Frequency and voltage

Q4. Perfect reproducibility means the instrument has:
(a) Zero drift
(b) Minimum accuracy
(c) High accuracy
(d) Maximum drift

Q5. A wattmeter has a full-scale range of 2500 watt. It has an error of 1% of true value. What would be the range of reading if true power is 1250 watt?
(a) 1200 – 1300 watt
(b) 1225 – 1275 watt
(c) 1237.5 – 1262.5 watt
(d) 1245 – 1255 watt

Q6. To distinguish between signals having very close values, we need an instrument with:
(a) High sensitivity
(b) High accuracy
(c) High resolution
(d) High linearity

Q7. The error committed by a person in the measurement are –
(a) Gross error
(b) Instrumental error
(c) Environmental error
(d) Random error

Q8. A moving coil permanent magnet instrument can be used as flux-meter:
(a) By using a low resistance shunt
(b) By eliminating the control springs
(c) By using a high series resistance.
(d) By making control springs of large moment of inertia

Q9. Damping of deflecting type instrument is done to –
(a) Make the moving system fast
(b) Reduce the oscillation of the pointer in the final deflected position
(c) Make the moving system slow
(d) Reduce the angle of deflection of the pointer on the graduated scale

Q10. An accurate ammeter must have a resistance of:
(a) Very high value
(b) High value
(c) Low value
(d) Very low value

SOLUTIONS
S1. Ans.(b)
Sol. The multiplier and the meter coil in a voltmeter are connected in series. To increase the range of voltmeter, a high unsolicited resistance is connected in series with the voltmeter coil.

S2. Ans.(a)
Sol. To measure the rms value of an arbitrary waveform, we may feed an input signal to a heating element in close proximity to a thermocouple.

S3. Ans.(a)
Sol. CRT (Cathode Ray Tube) display Voltage and Period. It is a vacuum tube that contains one or more electron guns and a phosphorescent screen on which image is displayed. With the help of this instrument electron beams are modulated, accelerated, and deflected onto the screen. It is used in laboratories to study the reactions due to electrical and electronic circuit and to display, measure and analyses different waves.

S4. Ans.(a)
Sol. The reproducibility of the instrument is the degree of closeness with which a given value of quantity or condition can be repeatedly measured while approaching the measurement from both sides under the same operating conditions.
Perfect Reproducibility means that the instrument has no drift.

S5. Ans.(c)
Sol. Given:
Full scale range = 2500 watt
True power = 1250 watt
error = 1%
Here,
1% of true value = 1% of 1250 watt
⇒ 1% of true value = (1250 ×1)/100 = 12.5 watt
Now,
For + 1%, reading = 1250 + 12.5 = 1262.5 watt
and, For – 1% reading = 1250 – 12.5 = 1237.5 watt
So, the range of reading if true power is 1250 watt is 1237.5 – 1262.5 watt.

S6. Ans.(c)
Sol. Resolution is the degree to which a change can be theoretically detected, usually expressed as a number of bits. This relates the number of bits of resolution to the actual voltage measurements.

S7. Ans.(a)
Sol. Manual errors in reading instruments or recording and calculating measurement results are known as Gross errors. These errors occur due to fault or improper reading by person.

S8. Ans.(b)
Sol. A moving coil permanent magnet instrument can be used as flux-meter by eliminating the control springs.

S9. Ans.(b)
Sol. In a measuring instrument, the damping is done to bring the moving system to rest to indicate steady reflection in a reasonable short time.

S10. Ans.(d)
Sol. An ammeter is kept in series with the electrical circuit so that it can measure the full current of the circuit. Hence, a very low resistance is used in an accurate ammeter.

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