Short Answer TypeMention the function of any two of the following used in communication system:
(i) Transducer (ii) Repeater
(iii) Transmitter (iv) Band pass FilterThe current in the forward bias is known to be more (~mA) than the current in the reverse bias (~ A). What is the reason, then, to operate the photodiode in reverse bias?
(a) Using Bohr’s second postulate of quantization of orbital angular momentum show that the circumference of the electron in the nth orbital state in hydrogen atom is n times the de Broglie wavelength associated with it.
(b) The electron in hydrogen atom is initially in the third excited state.
What is the maximum number of spectral lines which can be emitted when it finally moves to the ground state?(i) What characteristic property of nuclear force explains the constancy of binding energy per nucleon (BE/A) in the range of mass number ‘A’ lying 30 < A < 170?
(ii) Show that the density of nucleus over a wide range of nuclei is constant- independent of mass number A.Write any two factor which justify the need for modulating a signal.
Draw a diagram showing an amplitude modulated wave by superposing a modulating signal over a sinusoidal carrier wave.Write Einstein’s photoelectric equation. State clearly how this equation is obtained using the photon picture of electromagnetic radiation.
Write the three salient features observed in photoelectric effect which can be explained using this equation.a) Why are coherent sources necessary to produce a sustained interference pattern?
(b) In Young’s double slit experiment using monochromatic light of wavelength 
, the intensity of light at a point on the screen where path difference is 
is K units. Find out the intensity of light at a point where path difference is 
.
Use Huygen’s principle to explain the formation of diffraction pattern due to a single slit illuminated by a monochromatic source of light.
When the width of slit is made double the original width, how this affect the size and intensity of the central diffraction band?
Long Answer TypeExplain the principle of a device that can build up high voltages of the order of a few million volts.
Draw a schematic diagram and explain the working of this device.
Is there any restriction on the upper limit of the high voltages set up in this machine? Explain.
Van de Graaff generator is capable of producing very high potential of the order of 10 MV.
The underlying principle of Van de graaf generator is that a charge given to a hollow conductor is transferred to outer surface and is distributed uniformly over it.
Construction: It consists of a large hollow metallic sphere S mounted on two insulating columns A and B and an endless belt of rubber or silk is made to run on two pulleys P1 and P2 by the means of an electric motor. C1 and C2 are two sharp metallic spikes in the form of combs. The lower comb C1 is connected to the positive terminal of a very high voltage source and the upper comb C2 is connected to the inner surface of metallic sphere S.
Working: When comb C1 is given very high potential, then it produces ions in its vicinity, due to action of sharp points. The positive ions, so produced, get sprayed on the belt due to the repulsion between positive ions and comb C1. These positive ions are carried upward by the moving belt. The pointed end of C2 just touches the belt. The comb C2 collects positive charge from the belt which immediately moves to the outer surface of sphere S. As the belt goes on revolving, it continues to take (+) charge upward, which is collected by comb C2 and transferred to outer surface of sphere S. Thus the outer surface of metallic sphere S gains positive charge continuously and its potential rises to a very high value.
When the potential of a metallic sphere gains very high value, the dielectric strength of surrounding air breaks down and its charge begins to leak, to the surrounding air. The maximum potential is reached when the rate of leakage of charge becomes equal to the rate of charge transferred to the sphere. To prevent leakage of charge from the sphere, the generator is completely enclosed in an earthed connected steel tank which is filled with air under high pressure.
Van de Graff generator is used to accelerate stream of charged particles to very high velocities. But, there is a restriction on the upper limit of high voltage set up in the machine. The high voltages can be built up to the breakdown field of the surrounding medium.
(a) Define electric flux. Write its S.I. units.
(b) Using Gauss’s law, prove that the electric field at a point due to a uniformly charged infinite plane sheet is independent of the distance from it.
(c) How is the field directed if (i) the sheet is positively charged, (ii) negatively charged?
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