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 Ω

Answer: (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 𝑊

Answer: (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 rpm

Answer: (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 𝑊

Answer: (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 Hz

Answer: (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 rpm

Answer: (c)

19. Which of the following are the engineering materials?

1. Metals and alloys

2. Ceramics and glasses

3. Organic polymers

(a) 1 and 2 only

(b) 1 and 3 only

(c) 2 and 3 only

(d) 1, 2 and 3

Answer: (d)

20. The volume of a Face-Centered Cubic (FCC) unit cell in terms of the atomic radius R will be:


Answer: (a)