Physics Paper VI Quantum Physics And Electronics Previous Year Question Paper Year 2005 : IIIrd Year
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.
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.
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.
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.
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.
Q. 6. Obtain an expression for Planck’s formula and deduce from it Rayleigh-Jeans law and Wien’s law.
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.
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.