#### 12th Standard Physics English Medium Electromagnetic Induction and Alternating Current Reduced Syllabus Important Questions 2021

12th Standard

Reg.No. :
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Physics

Time : 01:00:00 Hrs
Total Marks : 105
Multiple Choice Questions
15 x 1 = 15
1. An electron moves on a straight line path XY as shown in the figure. The coil abcd is adjacent to the path of the electron. What will be the direction of current, if any, induced in the coil?

(a)

The current will reverse its direction as the electron goes past the coil

(b)

No current will be induced

(c)

abcd

(d)

2. When the current changes from +2A to −2A in 0.05 s, an emf of 8 V is induced in a coil. Th e co-efficient of self-induction of the coil is

(a)

0.2H

(b)

0.4H

(c)

0.8H

(d)

0.1H

3. 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

4. An emf of 12V is induced when the current in the coil changes at the rate of 40 A S-1. The coefficient of self induction of the coil is

(a)

0.3 H

(b)

0.003 H

(c)

30 H

(d)

4.8 H

5. Transformer works on

(a)

AC only

(b)

DC only

(c)

both AC and DC

(d)

AC more effectively than DC

6. If a secondary coil has 40 turns, and a primary coil with 20 turns is charged with 50V of potential difference, then potential difference in secondary would be

(a)

50 V

(b)

25 V

(c)

60 V

(d)

100 V

7. A phenomenon in which a varying current in one coil induces an emf in the neighbouring coil is

(a)

mutual induction

(b)

self induction

(c)

electrostatic induction

(d)

electromagnetic induction

8. AC generator works on the principle of

(a)

self induction

(b)

mutual induction

(c)

electromagnetic induction

(d)

none of these

9. The property of a coil which enables to produce an opposite induced emf in it when the current in the coil changes is called _______________

(a)

electromagnetism

(b)

self - induction

(c)

mutual induction

(d)

parallel- induction

10. __________ principle is used in transformer.

(a)

mutual induction

(b)

electromagnetic induction

(c)

self induction

(d)

eddy currents

11. In a transformer, eddy current loss is minimized by using

(a)

(b)

(c)

shell type core

(d)

thick copper wire

12. Unit of inductive reactance is ___________

(a)

ohm-metre

(b)

mho-metre-1

(c)

ohm

(d)

mho

13. The power factor of an a.c, circuit is _________

(a)

$\phi$sin$\phi$

(b)

cosec $\phi$

(c)

cos $\phi$

(d)

tan $\phi$

14. In LCR series circuit, at resonance is ___________

(a)

impedance (Z) is maximum

(b)

current is minimum

(c)

impedance (Z) is equal to R

(d)

vo = $\frac{1}{LC}$

15. In RLC series AC circuit at resonance:

(a)

Resistance is zero

(b)

Net reactance is zero

(c)

impedance is maximum

(d)

voltage leads the current by a phase angle $\frac{ㅠ}{2}$

16. 2 Marks
10 x 2 = 20
17. Mention the ways of producing induced emf.

18. Give the principle of AC generator.

19. What are step-up and step-down transformers?

20. How will you define Q-factor?

21. Explain the use of transformers in long distance transmission of electric power

22. Distinguish between AC and DC.

23. Write the application of series RLC resonant circut

24. What is the signifienance of Quality factor or Q-factor.

25. A bar magnet is moved in the direction indicted by the arrow between two coils PQ and CD predict the directions of induced current in each coil.

26. Three ac circuits in which equal amount of circuits are flowing. If the frequency of emf is increased how will the current the affected in these circuits? Give reason.

27. 3 Marks
10 x 3 = 30
28. A cylindrical bar magnet is kept along the axis of a circular solenoid. If the magnet is rotated about its axis, find out whether an electric current is induced in the coil.

29. A straight conducting wire is dropped horizontally from a certain height with its length along east – west direction. Will an emf be induced in it? Justify your answer.

30. Show that Lenz’s law is in accordance with the law of conservation of energy.

31. Define self-inductance of a coil interms of
(i) magnetic flux and
(ii) induced emf.

32. What do you understand by self-inductance of a coil? Give its physical significance.

33. Show mathematically that the rotation of a coil in a magnetic field over one rotation induces an alternating emf of one cycle.

34. Explain the construction and working of transformer

35. Derive an expression for phase angle between the applied voltage and current in a series RLC circuit.

36. Distinguish between average & rms value of an AC.

37. How does the capacitive reactance depend on frequency? & What is the reactance of a capacitor at hertz to the study at?

38. 5 Marks
8 x 5 = 40
39. An ideal transformer has 460 and 40,000 turns in the primary and secondary coils respectively. Find the voltage developed per turn of the secondary if the transformer is connected to a 230 V AC mains. The secondary is given to a load of resistance 104 Ω. Calculate the power delivered to the load.

40. Find the impedance of a series RLC circuit if the inductive reactance, capacitive reactance and resistance are 184 Ω, 144 Ω and 30 Ω respectively. Also calculate the phase angle between voltage and current.

41. A closely wound coil of radius 0.02 m is placed perpendicular to the magnetic field. When the magnetic field is changed from 8000 T to 2000 T in 6 s, an emf of 44 V is induced. Calculate the number of turns in the coil.

42. A long solenoid having 400 turns per cm carries a current 2A. A 100 turn coil of cross-sectional area 4 cm2 is placed co-axially inside the solenoid so that the coil is in the field produced by the solenoid. Find the emf induced in the coil if the current through the solenoid reverses its direction in 0.04 sec.

43. When does power factor of a series RLC circuit become maximum?

44. Explain mechanical analogy ofLC oscillations by quantitative treatment.

45. An a.c voltage of 300V applied to the primary of a transformer & voltage of 3000V is obtained from the secondary coil. Calculate the ratio of circuit in the primary & secondary coils.

46. An AC generator consists of a coil of 1000 turns and cross. sectional area of 100 cm2, rotating at an angular speed of 100 rpm in a uniform magnetic field of 1.6 x 10-2 T calculate the maximum emf produced in the coil