Ques 91. The leakage resistance of a 50 Km long cable is 1 MΩ. For a 100 Km long cable it will be
1 MΩ
2 MΩ
0.5 MΩ
None of these
Answer.3. 0.5 MΩ
Explanation:
Leakage resistance of the cable α 1/Length
For 100 km long cable leakage resistance of cable
=50/100 =0.5MΩ
Ques 92. A series drawing an armature current of Is is operating under saturated magnetic conditions, the torque developed in the motor is proportional to
1/Ia
1/I2a
I2a
Ia
Answer.4. Ia
Explanation:
We know Torque Tα ΦIa As the motor is operating under saturation condition so torque will be independent of flux i.e. T α Ia.
Ques 93. The insulation resistance of a cable of length 10 Km is 1 MΩ. Its resistance for 50 Km length will be
1 MΩ
0.5 MΩ
0.2 MΩ
None of these
Answer.2. 0.2 MΩ
Explanation:
Insulation resistance of the cable
R α 1/Length
R2/R1 = L1/L2
Hence, insulation resistance for 50 km length
R2 = (1 × 10)/50
= 0.2 MΩ
Ques 94. When a line-to-ground fault occurs, the current in a faulted phase is 100 A. The zero sequence current in the case will be
Zero
33.3 A
66.6 A
100 A
Answer.2. 33.3 A
Explanation:
For LIne to ground fault, we know that
IN = If = 3Io
Where IN = Neutral current
If = Fault current
Io = zero sequence current
Hence zero sequence current is
100/3 = 33.3 A
Ques 95. A 3 phase, 400-V, 50 Hz 4 pole induction motor is fed from a 3-phase supply and runs of 1425 rpm. The frequency of the rotor emf is
2.5 Hz
50 Hz
48 Hz
Zero
Answer.1. 2.5 Hz
Explanation:
Synchronous speed
Ns = 120f/P
= 120 × 50/ 4
= 1500 rpm
Rotor speed = 1425 rpm
Slip = (Ns – Nr)/Ns
= (1500 – 1425)/1500
= 0.05
∴ Frequency of rotor emf
= 0.05 × 50
= 2.5 Hz
Ques 96. The field coils of a dynamo have an inductance of 8H and have a resistance of 60 ohms and are connected to 120 V dc source. The steady-state current in the field coiled is
15 A
2 A
0 A
None of these
Answer.2. 2A
Explanation:
Steady-state field current = 120/60 = 2A
Ques 97. The surge impedance of a 50 miles long underground cable is 50 ohms. For a 25 miles length, it will be
25 Ω
50 Ω
100 Ω
None of these
Answer.2. 50 ohms
Explanation:
Surge impedance is independent of the length of the line hence the surge impedance will remain 50 ohms
Ques 98. In a BJT with α = 0.98, β is equal to
49
98
0.49
980
Answer.1. 49
Explanation:
In CB mode current gain is
Ic/IE = α
In CC mode current gain is
β =IC/IB
and β = α (1 – α)
= 0.98/(1-0.98) = 49
Ques 99. Two coils in differential connection have self-inductance of 2 mH and 4 mH and a mutual inductance 0f 0.15 mH. The equivalent inductance of the combination is
5.7 mH
5.85 mH
6 mH
6.15 mH
Answer.1. 5.7 mH
Explanation:
Total inductance for differential connection is given as