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#### Important 3 Mark Book Back Questions (New Syllabus) 2020

12th Standard EM

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Physics

Time : 01:00:00 Hrs
Total Marks : 114

Part A

38 x 3 = 114
1. Calculate the number of electrons in one coulomb of negative charge.

2. A block of mass m and positive charge q is placed on an insulated frictionless inclined plane as shown in the figure. A uniform electric field E is applied parallel to the inclined surface such that the block is at rest. Calculate the magnitude of the electric field E.

3. Calculate the electric dipole moment for the following charge configurations.

4. Derive an expression for the torque experienced by a dipole due to a uniform electric field.

5. Obtain the expression for energy stored in the parallel plate capacitor.

6. Determine the number of electrons flowing per second through a conductor, when a current of 32 A flows through it.

7. Resistance of a material at 100C and 400C are 45 Ω and 85 Ω respectively. Find its temperature co-efficient of resistance.

8. Let the magnetic moment of a bar magnet be $\overset { \rightarrow }{ { p }_{ m } }$ whose magnetic length is d = 2l and pole strength is qm. Compute the magnetic moment of the bar magnet when it is cut into two pieces
(a) along its length
(b) perpendicular to its length.

9. Show the time period of oscillation when a bar magnet is kept in a uniform magnetic field is
$T=2\pi \sqrt { \frac { 1 }{ { p }_{ m }B } }$ in second, where I represents moment of inertia of the bar magnet, pm is the magnetic moment and is the magnetic field

10. The magnetic field shown in the figure is due to the current carrying wire. In which
direction does the current flow in the wire?.

11. Obtain a relation for the magnetic induction at a point along the axis of a circular coil carrying current.

12. What is tangent law? Discuss in detail.

13. A closed coil of 40 turns and of area 200 cm2, is rotated in a magnetic field of flux density 2 Wb m-2. It rotates from a position where its plane makes an angle of 30o with the field to a position perpendicular to the field in a time 0.2 sec. Find the magnitude of the emf induced in the coil due to its rotation.

14. A conducting rod of length 0.5 m falls freely from the top of a building of height 7.2 m at a place in Chennai where the horizontal component of Earth’s magnetic field is 40378.7 nT. If the length of the rod is perpendicular to Earth’s horizontal magnetic field, find the emf induced across the conductor when the rod is about to touch the ground. [Take g = 10 m s-2]

15. The self-inductance of an air-core solenoid is 4.8 mH. If its core is replaced by iron core, then its self-inductance becomes 1.8 H. Find out the relative permeability of iron.

16. Using Faraday’s law of electromagnetic induction, derive an equation for motional emf.

17. How are the three different emfs generated in a three-phase AC generator? Show the graphical representation of these three emfs.

18. Show that the total energy is conserved during LC oscillations.

19. The relative magnetic permeability of the medium is 2.5 and the relative electrical permittivity of the medium is 2.25. Compute the refractive index of the medium.

20. Write down the properties of electromagnetic waves.

21. Derive the equation for acceptance angle and numerical aperture, of optical fiber.

22. Explain the Young's double slit experimental setup and obtain the equation for path difference.

23. Explain the experimental determination of material of the prism using spectrometer.

24. Light travelling through transparent oil enters in to glass of refractive index 1.5. If the refractive index of glass with respect to the oil is 1.25, what is the refractive index of the oil?

25. The thickness of a glass slab is 0.25 m. it has a refractive index of 1.5. A ray of light is incident on the surface of the slab at an angle of 60o. Find the lateral displacement of the light when it emerges from the other side of the mirror.

26. If the focal length is 150 cm for a glass lens, what is the power of the lens?

27. Find the dispersive power of flint glass if the refractive indices of flint glass for red, green and violet light are 1.613, 1.620 and 1.632 respectily.

28. Explain how frequency of incident light varies with stopping potential.

29. Derive an expression for de Broglie wavelength of electrons.

30. Light of wavelength 390 nm is directed at a metal electrode. To find the energy of electrons ejected, an opposing potential difference is established between it and another electrode. The current of photoelectrons from one to the other is stopped completely when the potential difference is 1.10 V. Determine i) the work function of the metal and ii) the maximum wavelength of light that can eject electrons from this metal

31. Discuss the gamma decay process with example.

32. Explain in detail the four fundamental forces.

33. Calculate the average atomic mass of chlorine if no distinction is made between its different isotopes?

34. Write notes on Photodiode

35. State and prove De Morgan's First and Second theorems.

36. In a transistor connected in the common base configuration, α = 0.95, IB = mA. Calculate the values of IC and IB

37. Elaborate on the basic elements of communication system with the necessary block diagram.

38. Discuss the functions of key components in Robots?