Quiz: Electrical Engineering

Exam: UPSSSC JE

Topic: Measurement and measuring instrument

Each question carries 1 mark.

Negative marking: 1/4 mark

Time: 10 Minute

Q1. Swamping resistance is used to compensate error due to

(a)Stray magnetic field

(b)Temperature variations

(c)Large supply variations

(d)None of the above

Q2. Which of the following is an Integrating instrument?

(a) Watt-hour meter

(b) Ammeter

(c) Voltmeter

(d) Wattmeter

Q3. Induction type energy meter measures energy in _______:

(a) Joules

(b) kW

(c) kWh

(d) W

Q4. Creeping in a singly-phase induction type energy meter may be due to-

(a) Overcompensation for friction

(b) Over voltages

(c) Vibrations

(d) All of these

Q5. In two wattmeter method of power measurement method, the power factor is given as:

(a) sin{tan^(–1)(±√3 (W1 – W2)/(W1 + W_2 )) }

(b) cos{tan^(–1)(±√3 (W1+ W2)/(W1 – W2 )) }

(c) sin{tan^(–1)(±√3 (W1+ W2)/(W1 – W2 )) }

(d) cos{tan^(–1)(±√3 (W1– W2)/(W1+ W2 )) }

Q6. The minimum number of wattmeter(s) required to measure 3-phase. 3-wire balanced or unbalanced power is:

(a) 4

(b) 1

(c) 2

(d) 3

Q7. For increasing the range of voltmeter, connect a

(a) Low value resistance in series with voltmeter

(b) High value resistance in parallel with voltmeter

(c) High value resistance in series with voltmeter

(d) Low value resistance in parallel with voltmeter

Q8. A voltmeter must have very high internal resistance so that

(a) Accuracy is high

(b) Resolution is high

(c) Draws small amount of current

(d) Creates high loading effect of the circuit

Q9. Electrostatic instruments are suitable for the measurement of:

(a) ac and dc voltages

(b) ac voltage and current

(c) dc voltage and current

(d) ac and dc current

Q10. …….. voltmeter has the least power consumption.

(a)Electrostatic type

(b)Hot wire type

(c)Induction type

(d)Moving iron attraction type

SOLUTIONS

S1. Ans.(b)

Sol. The ammeter is a sensitive device which is easily affected by the surrounding temperature. The variation in temperature causes the error in the reading. This can reduce by swamping resistance. The resistance having zero temperature coefficient is known as the swamping resistance. It connects in series with the ammeter.

S2. Ans.(a)

Sol. integrating instrument are those instruments which measures the electrical quantity over a period.

S3. Ans.(c)

Sol. induction type works on AC. Due to series and shunt magnet eddy current induced on ‘Al’ disc, which interacts and provides rotation. The commercial unit of electrical energy is kilowatt-hour (KWh). For measurement of energy in a.c. circuit, the meter used is based on “electro-magnetic induction” principle. They are known as induction type instruments.

S4. Ans.(d)

Sol. Creeping in Energy meter: – Creeping is phenomena by which Al disc rotates continuously.

This is due to following reasons-

a) Pressure coil energized and current coil having no current.

b) due to over voltage and friction.

S5. Ans.(d)

Sol. power measurement by two wattmeter method –

tanθ = √3 ((W1-W2)/(W1+W2 ))

So, power factor =cosθ=cos{tan^(-1)±√3 ((W_1-W_2)/(W_1+W_2 ))}

And two wattmeter method used for-

I. balanced and unbalanced load

II. star and delta connected load.

S6. Ans.(c)

Sol. for n-wire system, minimum number of wattmeter required = (n-1)

S7. Ans.(c)

Sol. Voltmeter range increment: – High value resistance in series with it

I.e.(Rs=Rm (m-1) )

Rm = meter resistance

m=V/Vm≃I/Im

S8. Ans.(c)

Sol. voltmeter having high internal resistance so it draws low current and correctly measure the potential difference connected across the point a-b.

S9. Ans.(a)

Sol. Electrostatics instruments are suitable for only voltage (AC or DC) measurement.

Electrostatics instruments do not measure current, power energy etc.

S10. Ans.(a)

Sol. advantages of electrostatic type voltmeter:

Power consumption is quite low in these types of instruments as the current drawn by these instruments is quite low.

We can measure high value of voltage.

Suitable for voltage (ac or dc) measurement.