Quiz: Electrical Engineering 22 June 2020

Quiz: Electrical Engineering
Topic: Miscellaneous

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

Q1. The advantage of putting tapping at the phase ends of a Transformer is
(a) to obtain fine variation of voltage
(b) to operate with ease
(c) to reduce the no of bushing
(d) to obtain better regulation

Q2. The field of self-excited generator is excited by
(a) AC
(b) DC
(c) by its own current
(d) Either AC or DC

Q3. The main use of DC shunt motor for driving the
(a) train
(b) crane
(c) hoist
(d) machine tools

Q4. In DC shunt motors, as load is reduced then the speed will be
(a) increase abruptly
(b) increase in proportion to reduction in load
(c) remain almost constant
(d) reduce

Q5. The variable resister shunting the field of DC series motor is called
(a) Armature diverter
(b) voltage regulator
(c) potential diverter
(d) field diverter

Q6. A DC series motor is accidently connected to single phase ac supply. The torque produce will be
(a) of zero average value
(b) Oscillating
(c) steady and unidirectional
(d) pulsating and unidirectional

Q7. In case of DC series motor, it is possible to have finite no-load speed if a resistance is connected across its-
(a) Field terminals
(b) Armature terminals
(c) Field and armature together
(d) It is not possible

Q8. The current drawn by a 120 V DC motor of armature resistance 0.8 Ω and back emf 110 V is
(a) 12.5 A
(b) 24.5 A
(c) 22.4 A
(d) 10.5 A

Q9. If the variable losses in a DC motor is 500 W. then for maximum efficiency of the motor, the constant losses must be
(a) 250 W
(b) 450 W
(c) 650 W
(d) 500 W

Q10. Ward-Leonard system of speed control is NOT recommended for:
(a) frequent motor reversals
(b) very low speeds
(c) constant speed operation
(d) wide speed range

S1. Ans. (c)
Sol. to reduce the no of bushing

S2. Ans. (c)
Sol. The field of self-excited generator is excited by its own current.

S3. Ans. (d)
Sol. The main use of DC shunt motor is driving machine tools.

S4. Ans. (c)
Sol. In DC shunt motors, as load is reduced then the speed will be remaining almost constant.

S5. Ans. (d)
Sol. Field diverter

S6. Ans. (d)
Sol. pulsating and unidirectional

S7. Ans. (b)
Sol. Armature terminals

S8. Ans. (a)
Sol. We have relation in case of DC motor as V=E_b+I_a R_a
I_a=(V-E_b)/R_a = (120-110)/0.8=12.5 A
S9. Ans. (d)
Sol. According to the condition of DC motor maximum efficiency, Variable losses = Constant losses

S10. Ans. (c)
Sol. constant speed operation

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