Deendayal Upadhya Gorakhpur University 2007 set 1 - exam paper

Q. 14. A parallel plate capacitor, every with plate area A and separation d, is charged to a potential difference V. The battery used to charge it is then disconnected. A dielectric slab of thickness d and dielectric constant K is now placed ranging from the plates. What change, if any, will take place in

charge on the plates
electric field intensity ranging from the plates
capacitance of the capacitor.
Justify your ans in every case. three
Q. 15. State Kirchhoff's rules of current distribution in an electrical network.
Using these rules determine the value of the current in the electric circuit provided beneath. 3

Q. 16. Write the mathematical relation for the resistivity of a material in terms of relaxation time, number density and mass and charge of charge carriers in it. Explain, using this relation, why the resistivity of a metal increases and that of a semi-conductor reduces with rise in temperature. 3

Q. 17. discuss with the help of a labelled diagram the underlying principle and working of a step-up transformer. Why cannot such a device be used to step-up d.c. voltage ? 3

Or

Draw a labelled diagram of an a.c. generator. discuss briefly its principle and working. 3

Q. 18. provided beneath are 2 electric circuits A and B
compute the ratio of power factor of the circuit B to the power factor of circuit A. three

Q. 19. describe the term 'resolving power' of an astronomical telescope. How does it get affected on

increasing the aperture of the objective lens ?
increasing the wavelength of the light used ?
Justify your ans in every case. 3

Q. 20. Write any 4 characteristics of electromagnetic waves. provide 2 uses every of

Radio-waves
Micro-waves. three
Q. 21. In a plot of photoelectric current versus anode potential, how does

the saturation current vary with anode potential for incident radiations of various frequencies but identical intensity ?
the stopping potential vary for incident radiations of various intensities but identical frequency ?
photoelectric current vary for various intensities but identical frequency of incident radiations ?
Justify your ans in every case. three
Q. 22. compute the amount of energy released during the a-decay of
provided : 1. atomic mass of
2. atomic mass of
3. atomic mass of
Is this decay spontaneous ? provide cause. three

Q. 23. What is a digital signal ? discuss the function of modem in data communication. Write 2 advantages of digital communication. 3

Q. 24. Explain, with the help of a schematic diagram, the principle and working of a Light Emitting Diode. What criterion is kept in mind while choosing the semiconductor material for such a device ? Write any 2 advantages of Light Emitting Diode over conventional incandescent lamps. 3

Q. 25. Draw a labelled diagram of a moving coil galvanometer. State the principle on which it works. Deduce an expression for the torque acting on a rectangular current carrying loop kept in a uniform magnetic field. Write 2 factors on which the current sensitivity> of a moving coil galvanometer depend. 5

Or

State Biot-Savart legal regulations. Use it to derive an expression for the magnetic field at the centre of a circular loop of radius R carrying a steady current I. Sketch the magnetic field lines for such a current carrying loop. 5

Q. 26. elaborate coherent sources ? Why are coherent sources needed to produce interference of light ? provide an example of interference of light in everyday life. In Young's double slit experiment, the 2 slits are 0.03 cm apart and the screen is placed at a distance of 1.5 m away from the slits. The distance ranging from the central bright fringe and 4th bright fringe is one cm. compute the wavelength of light used. 5

Or

State the condition under which the phenomenon of diffraction of light takes place. Derive an expression for the width of the central maximum due to diffraction of light at a single slit. A slit of width 'a' is illuminated by a monochromatic light of wavelength 700 nm at normal incidence. compute the value of 'a' for position of

first minimum at an angle of diffraction of 30°.
first maximum at an angle of diffraction of 30°. five
Q. 27. State the principle of working of p-n diode as a rectifier. Explain, with the help of a circuit diagram, the use of p-n diode as a full wave rectifier. Draw a sketch of the input and output waveforms. 5

Or

Draw the symbolic representation of a (i) p-n-p, (ii) n-p-n transistor. Why is the base region of transistor thin and lightly doped ? With proper circuit diagram, show the biasing of a p-n-p transistor in co mmon base configuration. discuss the movement of charge carriers through various parts of the transistor in such a configuration and show that . 5

Earning:   Approval pending.