Quiz: Electrical Engineering 1 June 2020

Quiz: Electrical Engineering
Topic: Measurement and measuring instrument
Each question carries 1 mark.
Negative marking: 1/4 mark
Time: 10 Minute

Q1. Horizontally mounted moving iron instruments employ
(a) eddy current damping
(b) air friction damping
(c) fluid friction damping
(d) electromagnetic damping

Q2. The deflecting torque of moving iron instrument is
(a) I^2 dL/dθ
(b) 1/2 I^2 dL/dθ
(c) I dL/dθ
(d) 1/2 I dL/dθ

Q3. Hysteresis error, in moving iron instruments, may be reduced by using
(a) mumetal or permalloy
(b) stainless steel
(c) silver coating
(d) high speed steel

Q4. A spring controlled moving iron voltmeter draws a current of 1 mA for full scale value of 100 V. If it draws a current of 0.5 mA the meter reading is
(a) 25 V
(b) 50 V
(c) 100 V
(d) 200 V

Q5. Moving coil permanent magnet instrument can be used for the measurement of
(a) AC and DC
(b) AC only
(c) DC only
(d) half wave rectified DC

Q6. An advantage of PMMC instrument is that it
(a) is free from friction error
(b) has high torque to weight ratio of moving parts
(c) has low torque to weight ratio
(d) can be used on both AC and DC

Q7. The term artificial aging in instrument is associated with
(a) springs
(b) permanent magnets
(c) controlling torques
(d) both (a) and (b)

Q8. A PMMC voltmeter is connected across a series combination of a dc voltage source V1 = 2V and an ac voltage source V2(t)= 3 Sin (4t) volts. The meter reads
(a) 2 V
(b) 5 V
(c) (2+√3/2)V
(d) √17/2 V

Q9. Which of the following meters does not exhibit square law response?
(a) Moving coil
(b) Moving iron
(c) Electrodynamometer
(d) hot wire instrument

Q10. Which of the following instrument is commonly used to measure primary current of a transformer connected to mains?
(a) Electrostatic meter
(b) Current transformer
(c) Moving coil type meter
(d) Moving iron meter

S1. Ans. (b)
Sol. air friction damping

S2. Ans. (b)
Sol. The correct relation for torque in moving iron is 1/2 I^2 dL/dθ.

S3. Ans. (a)
Sol. mumetal or permalloy

S4. Ans. (a)
Sol. Deflection, θ∝I^2
So, V∝I^2
V2 = V1 ((I^2 2)/(I^2 1)), putting the value in equation we get as the result
V2 = 25 V
S5. Ans. (c)
Sol. Moving coil permanent magnet instrument can be used for the measurement of DC only.

S6. Ans. (b)
Sol. has high torque to weight ratio of moving parts.

S7. Ans. (d)
Sol. Both spring and controlling torque are associated with term aging.

S8. Ans. (a)
Sol. The average value of ac current is zero so the instrument will measure 2 V .

S9. Ans. (a)
Sol. Moving iron

S10. Ans. (d)
Sol. Moving iron meter


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