Physics Paper VI Quantum Physics And Electronics Previous Year Question Paper Year 2005 : IIIrd Year

PART ‘A’

Q. 1. (a) What is thermionic emission ? Define thermionic work-function. 1,2
(b) What is space charge effect ? Discuss how does it limit the plate current. 1, 2
(c ) Describe with the help of a neat circuit diagram how the I-V characteristics of a pentode can be obtained. Compare these characteristics with output characteristic curves of a transistor.
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Q. 2. (a) Discuss how a barrier potential is formed in a p-n junction diode. How does it depend upon forward and reverse biasing ? 2, 2
(b) Describe the working of a full-wave rectifier. Obtain expressions for its ripple factor and efficiency.
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Q. 3. (a) What is a class-A amplifier ? Obtain an expression for gain of a class A voltage amplifier using a triode. 1, 7
(b) In a two-stage amplifier, using identical stages an a.c. signal of 0.2 V produces an a.c. output of 12.8 V. Determine the gain at each stage.
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Q. 4. (a) What do you understand by feedback in amplifiers? Obtain an expression for producing sustained oscillations. 1,4
(b) What are p- and n-type semiconductors ? Explain transistor action in an NPN transistor.
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PART ‘B’

Q. 5. (a) Obtain an expression for wavelength of de Broglie waves. 2
(b) What is the wavelength of matter-waves asociated with an electron accelerated (from rest) through a potential difference of 1.21 kV ? 2
(c ) Describe an experiment to establish the concept of de Broglie wavelength of an electron.
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Q. 6. Obtain an expression for Planck’s formula and deduce from it Rayleigh-Jeans law and Wien’s law.
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Q. 7. (a) Derive Schrodinger wave equation and obtain the eigenvalues for a square-well potential of infinite height. 5, 2
(b) Explain the significance of wave-function.
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Q. 8. Write notes on any two of the following :
(a) Heisenberg’s uncertainty principle;
(b) Harmonic oscillator and its eigenvalues;
(c ) Group and phase velocity.
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