SHORT ANSWER QUESTIONS

UNIT I

1.   Explain de Broglie hypothesis and write an equation for de Broglie wavelength.

2.   What is black body radiation?

3.   Define the photoelectric effect.

4.   Explain Planck’s radiation law.

5.   Explain the Heisenberg’s uncertainty principle.

UNIT II

1.   Define the effective mass of an electron and write an expression for it.

2.   Explain the formation of energy bands in solids.

3.   Distinguish between conductor and insulator.

4.   Distinguish between conductor and semiconductor.

5.   Distinguish between semiconductor and insulator.

UNIT III

1.   Distinguish between intrinsic and extrinsic semiconductors.

2.   Distinguish between n-type and p-type semiconductors.

3.   Write any four applications of the Hall effect.

4.   Explain the effect of temperature on the Fermi level in n-type semiconductors.

5.   Explain the effect of temperature on the Fermi level in p-type semiconductors.

 UNIT IV

1.      Explain spontaneous and stimulated emission.

2.      Explain population inversion in lasers.

3.      What are the characteristics of laser.

4.      Write any four applications of lasers.

5.      Explain the basic principle used in optical fiber for transmission of light.

UNIT V

1.      Explain electric polarizability and susceptibility.

2.      Explain ferroelectricity.

3.      Describe hysteresis loop in ferromagnetic material.

4.      Mention any two applications of magnetic materials.

5.      Mention any two applications of dielectric materials.

Long answer questions:

UNIT I

1.    Explain de Broglie wavelength and derive an equation for de Broglie wavelength in terms of kinetic energy.

2.    Explain black body and it’s radiation spectrum.

3.    Describe Davisson and Germer’s experiment for the study of electron diffraction.

4.    Derive time-independent Schrodinger’s wave equation and explain the significance of wave function.

5.    Derive Eigen values and Eigen functions for a particle in a one-dimensional potential box.

UNIT II

1.   Explain Bloch’s theorem.

2.   Explain the Kronig - Penny model of solids and show that it leads to energy band structure.

3.   What are Brillouin Zones? Explain using the E-K diagram.

4.   Explain the concept of the effective mass of an electron and derive an expression for it.

5.   Explain the classification of materials into insulators, semiconductors and conductors based on band theory.

UNIT III

1.    Derive an expression for electron concentration in an intrinsic semiconductor.

2.    Derive an expression for hole concentration in an intrinsic semiconductor.

3.    Derive an expression for carrier concentration in n-type semiconductor and explain the variation of Fermi level with temperature and concentration of dopants in n-type semiconductors.

4.    Derive an expression for carrier concentration in p-type semiconductor and explain the variation of Fermi level with temperature and concentration of dopants in p-type semiconductors.

5.    Explain Hall Effect and derive an expression for the Hall coefficient.

UNIT IV

1.  Describe the construction and working of the Nd-YAG laser with necessary diagrams.

2.      Explain the construction and working of He-Ne laser with necessary diagrams.

3.  Explain acceptance angle and derive an expression for acceptance angle of an optical fiber. How it is related to Numerical aperture?

4.  Differentiate step index and graded index optical fibers

5.      Explain different types of attenuations in optical fibers.

UNIT V

1.      Explain Electronic polarization and derive an expression for electronic polarizability.

2.      Explain Ionic polarization and derive an expression for ionic polarizability.

3.      Explain the classification of magnetic materials.

4.      Explain Ferromagnetic hysteresis loop on the basis of domain theory of ferromagnetism.

5.      Differentiate soft and hard magnetic materials and mention any two applications of each.

Tutorials

UNIT-I

1.  The work function for Cadmium is 4.08 eV, what must be the wavelength of radiation incident on Cadmium, so that maximum velocity of photo-electrons will be 7.2 x 105 m/s?

2.  The de-Broglie wavelength associated with an electron is 0.1 Å. Find the potential difference by which the electron is accelerated.

3.  Calculate the energy difference between the ground state and the first excited state for an electron in a box of length 1 Å.

4.  An enclosure filled with helium is heated to 400K. A beam of He atoms emerges out of the enclosure. Calculate the de Broglie wavelength corresponding to He atoms. Mass of He atom is 6.7×10-27 kg.

5.  Calculate the de Broglie wavelength of an electron of energy 100 eV.

6.  An electron is accelerated through a potential of 5000 V. Calculate the de Broglie wavelength of matter wave associated with it and its energy.

7.  If the uncertainty in position of an electron is 4×10-10 m. Calculate the uncertainty in its momentum.

8.  Calculate the wavelength of a 60g ball moving with a speed of 80m/s.

UNIT-III

1.  A pure semiconductor has charge concentration 5 x 1019 carriers/m3 at room temperature. Find the conductivity and resistivity of the semiconductor. The mobilities of electron and holes are 0.4 and 0.2 m2/V-s respectively.

2.  Calculate the intrinsic carrier concentration and conductivity at 300 K in germanium having energy gap 0.72 eV. Mobilities of electrons and holes are 0.4 and 0.2 m2/V-s respectively.  [m*e=m*h=m0].

3.  Calculate the intrinsic concentration of charge carriers of Germanium at 300K. Eg for Germanium is 0.67 eV.  [m*e=0.12mo & m*h=0.28mo, where mo=9.1×10-31Kg]

4.  In a Hall coefficient experiment, a current of 0.25A is sent through a metal strip having thickness of 0.2 mm and width 5 mm. The Hall voltage is found to be 0.15 mV when a magnetic field of 2000 Gauss is used. What is the carrier concentration?

5.  The RH of a specimen is 3.66 x 10-4 m3/C. its resistivity is 8.93 x10-3Ωm. Find the carrier concentration(n) and mobility (µ).

6.  A copper strip 2.0cm wide and 1.0mm thick is placed in a magnetic field with B=1.5 wb/m2. If a current of 200 A is set up in the strip, calculate Hall voltage that appears across the strip. Assume RH=6×10-7m3/C.

UNIT-IV

1.  The numerical aperture of an optical fiber is 0.39. If the difference in the refractive indices of the material of its core and the cladding is 0.05, calculate the refractive index of material of the core.

2.  Calculate the numerical aperture and acceptance angle for an optical fiber with core and cladding refractive indices being 1.48 and 1.45 respectively.

3.  A signal of 100 mW is injected into a fiber. The out coming signal from the other end is 40 mW. What is the loss in dB?

4.  Calculate the numerical aperture and acceptance angle for an optical fiber with core and cladding refractive indices being 1.50 and 1.48 respectively.

UNIT-V

1.  Find the Relative permeability of a ferromagnetic material if a field of strength 220 amp/m produces a magnetization 3300 amp/m in it.

The magnetic field intensity in a piece of oxide is 106 amp/m. If the susceptibility of the materials is 1.5×10-3, calculate the magnetization of the material