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Solid State Physics

An empty freight car with a mass of 10,000 kg rolls at 5 m/s along a level track and collides with a loaded car

with a mass of 20,000 kg, standing at rest with breaks released. Friction can be neglected. If the cars couple

together, find their velocities after the collision.

b) Find the decrease in kinetic energy as a result of the collision.

c) With that speed should the loaded car be rolling toward the empty car for both to be brought to rest

collision?

Solid State Physics

a stone is thrown horizontally from the roof of a building 15 m high with an initial speed of 5 m/s. How long will it take before the ball hits the ground?

Solid State Physics

Find the electric flux in a sphere of radius 0.48 cm from a charge of 55 nC.

Solid State Physics

What is Lorentz number? The thermal and electrical conductivities of Cu at 20^{o}C are 390 Wm^{-1}K^{-1 }and

5.87x10^{7}W^{-1}m^{-1} respectively. Calculate Lorentz number.

Solid State Physics

a fixed mass of gas at costant presure has a volume of 100°c find its volume at temperature of 54°c

Solid State Physics

Earth orbits the sun once every 365.25 days.

Find the average angular speed of Earth

about the sun.

Answer in units of rad/s.

Solid State Physics

**Question 5**

5.1 The electron and hole mobilities in a Si sample are 0.135 and 0.48m^{2}/V-s respectively. Determine the conductivities of intrinsic Si at 300 K if the intrinsic carrier concentration is 1.5x10^{6 }atom/m^{3}. The sample is then doped with 10^{23} phosphorus atom/m^{3}. Determine the equilibrium hole concentration, conductivity, and position of the Fermi level relative to the intrinsic level.

5.2 Indicate on an energy level diagram the conduction and valence bands, donor and acceptor states and the position of Fermi level for

(i) an intrinsic semiconductor.

(ii) a n-type semiconductor.

(iii) a p-type semiconductor.

Solid State Physics

**Question 3**

If the velocity of sound in a solid is of the order 10^{3} m/s, compare the frequency of the sound wave λ = 20 Å for (a) a monoatomic system and (b) acoustic waves and optical waves in a diatomic system containing two identical atoms (M=m) per unit cell of interatomic spacing 2.2 Å.

**Question 4**

4.1 The conductivity of silver is 6.5 x10^{7 }per Ohm per m and number of conduction electrons per m^{3 }is 6x10^{28 }Find the mobility of conduction electrons and the drift velocity in an electric field of 1 V/m. Given m = 9.1 x 10^{-31}kg and e=1.602 x 10^{-19}C.

4.2 What is Lorentz number? The thermal and electrical conductivities of Cu at 20^{o}C are 390 Wm^{-1}K^{-1 }and 5.87x10^{7}W^{-1}m^{-1} respectively. Calculate Lorentz number.

Solid State Physics

** Question 1**

Compute the net potential energy of a simple Na^{+}Cl^{- }pair. The equilibrium distance between the ions is 0.28nm. The potential energy due to repulsion between electrons is given by U_{r}= β/r^{8}

**Question 2**

*2.1* *α-Co *has an *hcp *structure with lattice spacings of *a= *2.51 A^{o }and c = 4.07 A^{o}, β *Co *is *fcc, *with a cubic lattice spacing of 3.55 A^{o}. What is the difference in density between the two forms?

2.2 Sodium transform from bcc to hcp at about T = 23K. Assuming that the density remains fixed, and the c/ *a *ratio isideal, calculate the *hcp *lattice spacing given that the cubic lattice spacing is *a' *= 4.23 A^{o }in the cubic phase.

Solid State Physics

Indicate on an energy level diagram the conduction and valence bands, donor and acceptor states and the position of Fermi level for

(i) an intrinsic semiconductor.

(ii) a n-type semiconductor.

(iii) a p-type semiconductor.