Physics – Important Questions Bank for Meghalaya Board (MBOSE) HSSLC 2016 Examination

PHYSICS

All questions are compulsory.

Use the following values of physical constants wherever necessary :

Speed of light in vacuum, c = 3 X 10 ⁸ ms ^{– 1}

Planck’s constant, h = 6.63 X 10 ^-34 J-s

Permittivity of free space, ƹ _o = 8.86 X 10 –¹² C₂ N^-1 m^-2

Permeability of free space, µ o = 4 π x 10^-7 T M A ^-1

Mass of electron, me = 9.11 x 10 ^-31 Kg

Mass of proton, mp = 1.67 x 10-²⁷ Kg

Electronic charge, e = 1.6 x 10^-19 C

Long answer type questions: Answer the following questions in 70 to 80 words each :

1. What is sky-wave propagation? Obtain an expression for the coverage range in space-wave propagation in terms of the height of the antenna.
2. Discuss two factors responsible for the need for modulation in communication.
3. What are semiconductors? Discuss the formation of depletion layer and potential barrier in an unbiased p-n junction diode.

4. Derive an expression for the magnitude of electric field intensity at a point on the equatorial line of an electric dipole. Also write the expression in vector form. Show that at a given distance from the centre of a short electric dipole, the magnitude of electric field intensity on the axial line is twice that of the equatorial line.

5. With the help of a diagram, briefly describe the construction and working of a cyclotron. Also find(a) the radius of the circular path and(b) the time period of revolution of an ion in a cyclotron.
6. Using the Biot-Savart law, find an expression for the magnetic field at the centre of a circular coil of radius r and carrying a current I .
7. Find an expression for the force per unit length between two parallel wires carrying current in the same direction. Hence, define an ampere.
8. State the Huygens’ principle for the wave theory of light. Using this principle, verify either the laws of reflection or the laws of refraction of light.
9. State the Ampere’s circuital law. Use the law to find the magnitude of the magnetic field inside a long, straight, air-cored solenoid. Also write the expressions for the magnitude of magnetic field(i) at points near the ends of the solenoid and(ii) inside the solenoid when it is iron-cored.
10. State and prove Brewster’s law and hence show that if ray of light is incident on the refracting surface at a polarising angle, then the reflected and refracted rays are perpendicular to each other.
11. Show that the magnitude of the electric field at an axial point far away from a short electric dipole is inversely proportional to the cube of its distance from the centre of the dipole.
12. With a neat circuit diagram, explain how the internal resistance of a cell can be determined by using a potentiometer.
13. Describe the working of a moving-coil galvanometer and hence show that the deflection of the coil is directly proportional to the current flowing through it.
14. Discuss the construction of an AC generator with the help of a simple diagram.
15. Using Huygens’ principle, establish the laws of reflection.
16. What is meant by interference of light? Give any two conditions for obtaining sustained interference pattern of light. Why two separate light bulbs cannot produce a sustained interference pattern of light?
17. What is photoelectric effect? Explain the variation of photoelectric current with the—(a) intensity of the incident light;(b) frequency of the incident light.
18. With the help of a neat diagram, deduce the condition for balance in a Wheatstone’s bridge by applying Kirchhoff’s laws.
19. Write down the condition of resonance in a series L-C-R circuit and hence find an expression for the resonant frequency. Also draw the resonance curve in L-C-R circuit.
20. What is the principle on which a transformer is based? With a simple diagram, briefly describe the working of a transformer.
21. Write any four properties of electromagnetic waves. Give two uses of microwaves.
22. Find an expression for the combined focal length of two thin coaxial convex lenses placed in contact.
23. Draw a labelled diagram to show the image formation at the near point due to a compound microscope and  hence calculate its magnifying power.
24. Deduce the expression for de Broglie wavelength of an electron accelerated through a potential difference of V volts. Hence find the de Broglie wavelength in Å associated with an electron accelerated under a potential difference of 100 volts.
25. Define half-life of a radioactive substance. Show that half-life of a radioactive substance inversely proportional to the decay constant.
26. Write down the postulates of Bohr’s theory of hydrogen atom.
27. What is intrinsic semiconductor? Name the type of extrinsic semiconductor obtained when germanium is doped with(i) arsenic and(ii) gallium.
28. Draw a neat diagram for a full-wave rectifier circuit.
29. Two point charges -q and +q separated by a short distance 2a are placed in free space at points A and B respectively. Derive an expression for the electric potential at a point P whose distance from the centre O of the line AB is r and OP makes an angle q with the electric dipole moment potential if P lies on(i) axial line and (ii) equatorial line.
30. State the Ampere’s circuital law. Use the law to find the magnitude of the magnetic field inside a long, straight, air-cored solenoid. Also write the expressions for the magnitude of magnetic field(i) at points near the ends of the solenoid and(ii) inside the solenoid when it is iron-cored.
31. What are isotones? Give example.
32. Represent the spectral series of H-atom by a neat energy-level diagram.
33. State and explain Lenz’s law.
34. What are eddy currents? How are eddy current losses minimized in a transformer?
35. Using Gauss’s theorem in electrostatics, obtain an expression for the electric field at a point outside a uniformly charged spherical shell.
36. When the current through a coil changes at the rate of 1 A/s, it induces a voltage of 1 m V. What is the  coefficient of self-induction of the coil?

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