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#### Electromagnetic Induction and Alternating Current Model Question Paper

12th Standard EM

Reg.No. :
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Physics

Time : 02:00:00 Hrs
Total Marks : 50
5 x 1 = 5
1. Th e fl ux linked with a coil at any instant t is given by $\Phi$B =10t2−50t+ 250 . The induced emf at t = 3s is

(a)

−190 V

(b)

−10 V

(c)

10 V

(d)

190 V

2. In a transformer, the number of turns in the primary and the secondary are 410 and 1230 respectively. If the current in primary is 6A, then that in the secondary coil is

(a)

2 A

(b)

18 A

(c)

12 A

(d)

1 A

3. In an electrical circuit, R, L, C and AC voltage source are all connected in series. When L is removed from the circuit, the phase difference between the voltage and current in the circuit is $\frac{\pi}{3}$. Instead, if C is removed from the circuit, the phase difference is again  $\frac{\pi}{3}$.  The power factor of the circuit is

(a)

1/2

(b)

1/$\sqrt2$

(c)

1

(d)

$\sqrt3$/2

4. An inductor 20 mH, a capacitor 50 μF and a resistor 40 Ω are connected in series across a source of emf v = 10 sin 340 t. The power loss in AC circuit is

(a)

0.76 W

(b)

0.89 W

(c)

0.46 W

(d)

0.67 W

5. $\frac{20}{\pi^2}H$inductor is connected to a capacitor of capacitance C. The value of C in order to impart maximum power at 50 Hz is

(a)

50 μF

(b)

0.5 μF

(c)

500 μF

(d)

5 μF

6. 5 x 1 = 5
7. Fleming's Right hand rule

8. (1)

Law of conservation of energy

9. Lenz's law

10. (2)

Predominantly Inductive

11. Ac circuit with resistor

12. (3)

13. Ac circuit with inductor

14. (4)

Voltage and current are in phase

15. RLC circuit

16. (5)

Generator rule

2 x 2 = 4
17. (a) Hysteresis loss
(b) Copper loss
(c) Flux loss
(d) Power loss

18. (a) Inductive reactance
(b) Self Inductance
(c) Capacitive reactance
(d) resistance

19. 2 x 1 = 2
20. (I) : An AC generator converts electrical energy into mechanical energy.
(II) : A Transformer converts high voltage (low current) into low voltage (high current) and vice versa. Which one is incorrect statement?
(a) I only
(b) II only
(c) both are correct
(d) None

21. (I) : In some AC generators, there are three separate coils, which would give three separate emfs. So they are called poly phase generato
(II) : Eddy current loss can be minimised by using shell type core
Which one is correct statement?
(a) I only
(b) II only
(c) both are correct
(d) None

22. 6 x 2 = 12
23. What is meant by electromagnetic induction?

24. State Lenz’s law.

25. Mention the ways of producing induced emf.

26. What is meant by mutual induction?

27. List out the advantages of stationary armature-rotating field system of AC generator.

28. Define average value of an alternating current.

29. 4 x 3 = 12
30. A circular antenna of area 3 m2 is installed at a place in Madurai. The plane of the area of antenna is inclined at 47o with the direction of Earth’s magnetic field. If the magnitude of Earth’s field at that place is 40773.9 nT find the magnetic flux linked with the antenna.

31. Give the uses of Foucault current.

32. Explain the construction and working of transformer

33. Give the advantage of AC in long distance power transmission with an example.

34. 2 x 5 = 10
35. The equation for an alternating current is given by i = 77 sin 314t. Find the peak value, frequency, time period and instantaneous value at t = 2 ms.

36. A square coil of side 30 cm with 500 turns is kept in a uniform magnetic field of 0.4 T. The plane of the coil is inclined at an angle of 300 to the field. Calculate the magnetic flux through the coil.