Problem 5

a) Show that green light (λ = 5 x 10-7 m) can excite electrons across the band gap of silicon (Si).

b) i. Electromagnetic radiation of frequency 3.091 x 1014 Hz illuminates a crystal of germanium (Ge). Calculate the wavelength photoemission generated by this interaction. Germanium is an elemental semiconductor with a band gap, Eg, of 0.7 eV. ii. Sketch the absorption spectrum of germanium, i.e., plot % absorption vs. wavelength, λ.

c) Potassium (K) and beryllium (Be) are metals which exhibit good electrical conductivity. Explain for both elements the reasons for the observed conductivity on the basis of the band structure.

d) A pure crystalline material (no impurities or dopants are present) appears red in transmitted light. i. Is this material a conductor, semiconductor or insulator? Give the reasons for your answer . ii. What is the approximate band gap (Eg) for this material in eV?

e) An unknown material is transparent to light of frequencies ( ν ) up to 1.3 x 1014 s–1 . Draw a meaningful schematic band structure for this material.

(This has to do with Physics)

6.1.1 How does a capacitor charge?

6.1.2 How does a capacitor discharge?

6.1.3 What is the time constant?

6.1.4 What are the units to τ?

How are research methodologies validated?

Two skydivers are holding on to each other while falling straight down at a common terminal speed of 63.10 m/s. Suddenly, they push away from each other. Immediately after separation, the first skydiver (who has a mass of 89.30 kg) has the following velocity components (with "straight down" corresponding to the positive z-axis):

v1x=4.93 m/s      v1y=3.75 m/s     v1z=63.1 m/s

What are the x- and y-components of the velocity of the second skydiver, whose mass is 57.70 kg, immediately after separation?

What is the change in kinetic energy of the system?

What are the specific contributors to both an internal and external force? Be specific related to passive and active structures.

A delta connected load has a parallel combination of resistance 5Ω and capacitive reactance –j5Ω in each phase. If a balanced three phase 400V supply is applied between lines, find the phase currents and line currents and draw the phasor diagram

A workshop with well-insulated walls and containing 450 m³ of air at 305 K is heated at constant pressure (atmospheric). Consider air to be an ideal diatomic gas.

(a)Determine the energy (in kJ) required to increase the temperature of the air in the building by 2.90°C.

How does the amount of heat required depend on the molar specific heat at constant pressure and the desired change in temperature? What is the value for the molar specific heat at constant pressure? How can you determine the number of moles of the gas? kJ

(b)Determine the mass (in kg) this amount of energy could lift through a height 3.10 m.

Explain the difference between Ekman and Sverdrup transport. How to diagram how these work in conjunction with zonal wind stress.

Show by derivatives that two phases are in thermal equilibrium only if their temperatures are the same. Show that two phases are in mechanical equilibrium only if their pressures are equal.   

A coaxial cable consists of two long concentric conducting tubes of length l, the inner one of radius a and the outer one of radius b. Assume that the zˆ direction lies along the axis of the cable. A current, I, flows down the inner conductor in the zˆ direction and returns in the outer conductor, where in each case the current is uniformly spread out over the surface.
(a) Determine the magnetic field B everywhere. [5]
(b) Find the self-inductance per unit length. [5]

In a cathode ray tube, electrons are accelerated from rest by a constant electric force of magnitude 6.40 × 10⁻¹⁷ N during the first 4.40 cm of the tube’s length; then they move at essentially constant velocity another 45.0 cm before hitting the screen.

a.How long does it take them to travel the length of the tube?

b.Find the speed of the electrons when they hit the screen.

c.How long does it take them to travel the length of the tube?

Summarize this experiment of pendulum from purpose to procedure to analysis.
Within your answer, include the theoretical equations.

Two protons, each having a speed of 0.910c in the laboratory, are moving toward each other.

a) Determine the momentum of each proton in the laboratory in GeV/c.

b) Determine the total momentum of the two protons in the laboratory GeV/c.

c) Determine the momentum of one proton as seen by the other proton GeV/c.

What is the difference between the root-mean-squared velocity (????) and the average velocity (?̅) of gas particles?