11. A resistance R is connected in series with a parallel combination of two resistances 12 Ω and 8 Ω. If the power dissipated in the circuit is 70 𝑊 when the applied voltage is 20 𝑉 across the circuit. The resistance 𝑅 will be nearly:
(a) 1.07 Ω(b) 0.91 Ω(c) 0.83 Ω(d) 0.75 ΩAnswer: (b)
12. A 120 𝑉 ac circuit contains 10 Ω resistance and 30 Ω reactance in series. The average power in the circuit will be nearly:(a) 134 𝑊(b) 144 𝑊(c) 158 𝑊(d) 168 𝑊Answer: (b)
13. A 25 ℎ𝑝, 250 𝑉 dc series motor has armature resistance of 0.1 Ω, field resistance of 0.05 Ω and brush contact drop 3 𝑉. When the line current is 80 𝐴, the speed is 600 rpm and when the line current is 100 𝐴, the speed will be nearly:(a) 394 rpm(b) 474 rpm(c) 556 rpm(d) 636 rpmAnswer: (b)
14. A 200/400-𝑉, 10-𝑘VA , 50 Hz single-phase transformer has at full-load a copper loss of 120 𝑊 . If it has an efficiency of 98 % at full-load unity power factor, the efficiency of the transformer at half load 0.8 power factor lagging will be:(a) 82 %(b) 87 %(c) 92 %(d) 97 %Answer: (d)
15. A 3- phase, 6- pole 50 Hz induction motor delivers 3.73 kW at 950 rpm . If the stator loss is 250 𝑊 , the stator input will be:(a) 4420 𝑊(b) 4340 𝑊(c) 4260 𝑊(d) 4180 𝑊Answer: (d)
16. In a 25 𝑘VA, 3300/230 𝑉, 1-phase transformer, the iron and full-load copper losses are respectively 350 𝑊 and 400 𝑊 . The efficiency at half load 0.8 power factor will be nearly:(a) 83 %(b) 88 %(c) 94 %(d) 99 %Answer: (d)
17. A 3-phase induction motor is wound for 4-poles and is supplied from a 50 Hz system. When speed of the rotor is 600 rpm, the rotor frequency will be:(a) 30 Hz(b) 35 Hz(c) 40 Hz(d) 45 HzAnswer: (a)
18. If a 6-pole induction motor running from a 50 Hz supply has an emf in the rotor of frequency 2.5 Hz. The speed of motor will be:(a) 910 rpm(b) 930 rpm(c) 950 rpm(d) 970 rpmAnswer: (c)
19. Which of the following are the engineering materials?1. Metals and alloys2. Ceramics and glasses3. Organic polymers(a) 1 and 2 only(b) 1 and 3 only(c) 2 and 3 only(d) 1, 2 and 3Answer: (d)
20. The volume of a Face-Centered Cubic (FCC) unit cell in terms of the atomic radius R will be:
Answer: (a)
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