Quiz: Electrical Engineering 03 July 2021

Quiz: Electrical Engineering
Exam: AE/JE
Topic: Miscellaneous

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

Q1. As resistance is added in the rotor circuit of a slip ring motor:
(a) if maximum torque increases but occurs at the same slip.
(b) its maximum torque decreases but occurs at the same slip.
(c) its maximum torque remains the same and also occurs at lower slip.
(d) its maximum torque remains the same but occurs at higher slip.

Q2. During no-load test an induction motor draws power:
(a) For core loss and windage and friction loss.
(b) for core loss and copper loss.
(c) for copper loss and windage and friction loss.
(d) only for the very small copper loss.

Q3. During short – circuit test on a slip ring in duction motor:
(a) the rotor is short – circuited but is free to rotate.
(b) rotor is short – circuited but is blocked from rotation.
(c) the rotor is open – circuited but is blocked from rotation.
(d) the rotor is open – circuited but is free to rotate

Q4. For type 2 system, the steady – state error due to ramp input is equal to
(a) zero
(b) finite constant
(c) infinite
(d) indeterminate

Q5. The type number of the control system with
G(s) H(s) = (K(s+2))/(s(s^2 2s+3)) is
(a) one
(b) two
(c) three
(d) four

Q6. Hysteresis is the phenomenon of __ in a magnetic circuit.
(a) Lagging B behind H
(b) Lagging H behind B
(c) Setting up constant flux
(d) None of these

Q7. An isolator is designed to open a circuit under
(a) full-load
(b) normal conditions
(c) no-load
(d) none of the above

Q8. An accurate ammeter must have a resistance of
(a) High value
(b) Low value
(c) Very low value
(d) Very high value

Q9. In the common collector configuration of bipolar junction transistor (BJT), the output voltage is
(a) Shifted by 270° from the input voltage
(b) In phase with the input voltage
(c) Out of phase with the input voltage
(d) Shifted by 90° from the input voltage

Q10. __ are difficult to measure using Wheatstone bridge.
(a) Higher resistances
(b) Currents
(c) Lower resistances
(d) Voltages

SOLUTIONS

S1. Ans.(d)
Sol. As resistance is added in the rotor circuit of a slip ring motor its maximum torque remains the same but occurs at higher slip.

S2. Ans.(a)
Sol. As the motor is running at no load, the total input power is equal to the constant iron loss, friction, and windage losses of the motor.

S3. Ans.(b)
Sol. The blocked rotor test of an induction motor is same as the short-circuit test of a transformer. In this test, the shaft of the motor is connected so that it cannot move and rotor winding is short-circuited. In a slip-ring motor, the rotor winding is short-circuited through slip-rings and in cage motors, the rotor bars are permanently short-circuited. This test is also called the locked-Rotor test.
Approx. model under block rotor test:

Blocked rotor slip, s=1
∴load resistance=R_2^’ (1/s-1)=R_2^’ (1/1-1)=0 (i.e., shorted)

S4. Ans.(a)
Sol. Velocity error coeff. kv=lim(s→0)⁡sG(s)H(s)=ꝏ
For type-2 ramp input, error=1/k_v =1/ꝏ=0

S5. Ans.(a)
Sol. Type of the system is determined by open loop pole at origin.

S6. Ans.(a)
Sol. The phenomenon of flux density B lagging behind the magnetizing force H in a magnetic material is known as Magnetic Hysteresis.

S7. Ans.(c)
Sol. Its main purpose is to isolate one portion of the circuit from the other and is not intended to be opened while current is flowing in a line. Such switches are generally used on both sides of circuit breakers in order that repairs and replacement can be made without any danger.

S8. Ans.(c)
Sol. An ammeter measures the value of current flowing in the circuit, so current should flow inside ammeter to give proper result. it acts like a closed switch so it indicates the current. And it has very low resistance to ensure the correct measurement of current in the circuit.

S9. Ans.(b)
Sol. In common collector configuration, Since the emitter is output terminal, it can be noted that the output voltage from a common collector circuit is the same as its input voltage. Hence the phase shift between the input voltage and the output voltage is 0°.

S10. Ans.(c)
Sol. Kelvin Bridge is used for measuring lower resistances.

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