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# DFCCIL Recruitment 2021

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## EXAM DATES

26 SEPT TO 30 SEPT

## DFCCIL’21 EE: Daily Practices Quiz

DFCCIL’21 EE: Daily Practices Quiz 21-Sep-2021

Each question carries 1 mark.
Negative marking: 1/4 mark
Total Questions: 06
Time: 08 min.

Q1. What is the relationship between the line voltage and the phase voltage in a delta -connected load?
(a) Line voltage = Phase current
(b) Line voltage > Phase voltage
(c) Line voltage < Phase voltage
(d) Line voltage = Phase voltage

Q2. An eight-pole wound rotor induction motor operating on 60 Hz supply is driven at 1800 rpm by a prime mover in the opposite direction of revolving magnetic field. The frequency of rotor current is:
(a) 60 Hz
(b) 200 Hz
(c) 120 Hz
(d) 180 Hz

Q3. A P– type crystal is obtained by doping
1. silicon with arsenic,
2. silicon with aluminium,
3. Ge with boron,
4. Ge with phosphorus.
(a) 2 and 3 are correct
(b) 2 and 4 are correct
(c) 1 and 4 are correct
(d) 1 and 3 are correct

Q4. The emf induced in the armature of a shunt generator is 600 V. The armature resistance is 0.1 ohm. If the armature current is 200 A, the terminal voltage will be:
(a) 620 V
(b) 580 V
(c) 600 V
(d) 640 V

Q5. In an induction motor, if the rotor resistance is equal to stand-still reactance then the maximum torque is…………
(a) Less than starting torque
(b) Equal to starting torque
(c) More than starting torque
(d) None of the above

Q6. Assertion (A): Shunt of an ammeter has a low resistance.
Reason (R): Shunt may be connected in series or parallel with ammeter.
(a) Both A and R are true and R is correct explanation of A
(b) Both A and R are true, but R is not correct explanation of A.
(c) A is true, R is false
(d) A is false, R is true

## SOLUTIONS

S1. Ans.(d)
Sol. In delta connected system the line voltage is equal to the phase voltage and the Line current is √3 times of Phase Current.

S2. Ans.(d)
Sol. N_s=120f/P=(120×60)/8
= 900 rpm
Now it is rotating in opposite direction so slip (S) = (900-(-1800))/900=3
Rotter frequency (Fr) = Sf
= 3×60
= 180 HZ

S3. Ans.(a)
Sol. Doping means the introduction of impurities into a semiconductor crystal to the defined modification of conductivity. In P-Type Semiconductor, the addition of trivalent impurities such as boron, aluminium or gallium to an intrinsic semiconductor creates deficiencies of valence electrons, called “holes”.

S4. Ans.(b)
Sol. For generator, V_t=E_g-I_a R_a=600-(200×0.1)=580 V.

S5. Ans.(b)
Sol. At maximum torque: slip(s)=R_2/X_2
If R_2=X_2, then s=1(starting slip)
So, if in an induction motor, if the rotor resistance is equal to stand-still reactance then the maximum torque is equal to starting torque.

S6. Ans.(c)
Sol. Shunt is connected in parallel with ammeter and has low value of resistance.

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