B.E. First Semester All Branches (C.B.S.) / B.E. First Semester (Fire Engineering)

Engineering Physics

1. Planck’s constant ‘h’= 6.63 ×10 ^{-34}JS

2. Velocity of light ‘C’ =3 ×10 ^{8}m/s

3. Charge on electron ‘e’ =1.602× 10^{-19} C

4. Mass of electron ‘m’ =9.11×10^{-31} kg

5. Avogadro’s constant ‘N_{A}‘= 6.023×10^{26} atoms/k mole

6. Boltzman’s constant ‘K’= 1.380 ×10^{-23} JK ^{-1}

1.a)Explain Compton effect. Write an expression for Compton Shift.

b)Write equations of conservation of energy and momentum in Compton effect.

c)Calculate de Broglie wavelength associated with an alpha particle accelerated by a potential difference of 25 K volts. (mass of a α particle =6.68×10^{-27} kg. Charge of a α particle = 3.2 x 10^{-19}C)

**OR**

2.a)Describe in detail, Davisson and Germer’s experiment to verify de Broglie hypothesis.

b)Show that a free electron can not absorb a photon completely.

c)A beam of X-rays is Scattered by loosely bound electrons at 450 from the direction of beam. The wavelength of Scattered X-rays is 0.22 A^{0}. What is the wavelength of incident X-rays?

3.a)Define phase velocity and group velocity of a wave packet. What is wave packet?

b)State Heisenberg’s uncertainty principle and verify it with the help of thought experiment of electron diffraction through single slit.

c)An electron has a speed of 300m/s accurate to 0.001%. What is the minimum accuracy with which its position can be located?

**OR**

4.a)Show that the wave function for a particle confined to one dimensional potential well of width ‘l’ is given by ψ_{n}(x)=\sqrt{\frac{2}{l}}sin\left ( \frac{n\pi x}{L} \right ) where symbols have their usual meanings.

b)Explain the phenomenon of Barrier tunneling”.

c)An electron is trapped in 1-dimensional box of length 0.1nm. Calculate energy of first and third allowed energy state.

5.a) Define the terms: i) Space lattice iii) Void space ii)Coordination no.

b)Find expressions for atomic radii of FCC and BCC structures.

c)Nickel crystallizes in a FCC crystal. The edge of a unit cell is 3.52 A^{0}. The atomic weight of Nickel is 58.710. Determine the density of Nickel.

**OR**

6.a)Define “Miller Indices” and draw planes in cubic system having Miller indices (110) and (121).

b)Deduce relation between interplanar spacing and miller indices for a cubic crystal.

X-rays with a wavelength of 1.54 A are used to calculate the spacing of (200) planes in aluminum. Bragg angle for this reflection is 22.4o. What is the size of unit cell of aluminium crystal?

*7.*a)3Show that for an intrinsic semiconductor the Fermi energy level lies at the middle of the band gap.

b)Show that barrier potential is given by V_{0}=\frac{kT}{e}ln\left ( \frac{N_{A}.N_{D}}{n_{i}^{2}} \right )where symbols have their usual meanings.

c)A strip of n-type germanium of width 0.5mm and thickness 1mm has a Hall coefficient 10 ^{2}m ^{3}/C. If the magnetic field used is 0.11 and current through the sample is 1mA, determine the Hall voltage produced.

**OR**

8.a)Derive expression for “Hall voltage” in Hall effect. Also define and find expression for “Hall coefficient”.

b)Draw energy band diagram for Biased npn transistor.

c)For npn transistor connected in CB mode, the emitter current is 3mA and base current is 25uA. Find the values of collector current and current gain.

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