Reading Quiz

Question 1:

Answer:

1. The Otto cycle and the Diesel engine. The Diesels are more efficient.
2. The Otto cycle and the Diesel cycle are used in internal combustion engines. At the same compression ratio, the Otto cycle is more efficient, but in practice Diesel cycle engines have higher compression ratios and hence are more efficient.
3. In an internal compustion engine, the Otto Cycle and the Diesel Cycle. The Diesel cycle is more efficient.
4. Otto cycle and diesel cycle. For a particular compression ratio, the otto cycle is more efficient; however a diesel engine is more efficient under operational conditions.
5. the two cycles are the compression and the power, with the power being more efficient.
6. The two cycles discussed here are the Otto and Disel cycle. Forr a given compression ratio the Otto cycle is more efficient, but the Disel cycle allows you to go to higher compression ratios, thus it can possibly have a higher efficiency.
7. Internal combustion engines use either the Otto cycle or Diesel cycle. For a given compression ratio, the Otto cycle is more efficient, but Diesel engines generally have higher compression ratios and hence higher efficiencies.
8. The Otto Cycle and a diesel engine. The diesel engine is more efficient because of its higher compression ratio (in reality). For the same compression ratio, the Otto Cycle is more efficient.
9. There is the Otto cycle, which is used as a gasoline engine in many cars, and there's the diesel engine. The diesel engine is more efficient than the Otto cycle because instead of compressing the fuel mixture (which might preignite at high temperatures), the diesel engine compresses the air then injects the fuel into the cylinder to ignite it.
10. Otto Cycle and Diesel Cycle the Otto Cycle is more efficient
11. The Otto cycle and the Diesel cycle. The diesel cycle is more efficient.

Question 2:

Answer:

1. You can't calculate the efficiency straight from the PV diagram because the last transition involves the liquid phase. Instead, you can use "steam tables" to look up proper values of enthalpy. Enthalpy is related to efficiency by equation (4.12)
2. The Rankine cycle doesn't use an ideal gas as its working substance. You need to write the heat in terms of the enthalpy and look the enthalpy up in a table to calculate the efficiency of the Rankine cycle.
3. You can't calculate the efficiency of the Rankine cycle straight from the PV diagram because the working substance is not an ideal gas: it turns into a liquid partway through the cycle. To calculate it, you need the pressures everywhere, the temperature when it is entirely steam in between the boiler and the turbine, (point 3 on Fig. 4.8,) and "steam tables."
4. A gas is not the working substance for the entire cycle, but enthalpy values for water and steam can be found in a table and used in the formula, e = 1 -(H4-H1)/(H3-H1)
5. Because the steam is not an ideal gas! Additionally it condenses during the cycle. Instead of using a pv diagram, you have to look up the efficiencies in tables.
6. It doesn't work to calculate efficiency from the PV diagram because the water becomes a liquid in the process, which is definetly not an ideal gas. What you need to use instead is the enthalpy's at each individual points.
7. The efficiecy is complicated to calculate because the gas condenses into liquid during the cycle. Instead, we can use steam tables to look up the data we need to compute efficiency.
8. Because the gas condenses down to a liquid! Instead you have to use enthalpy, since heat is expelled and absorbed at constant pressure.
9. You can't compute the efficiency straight from the PV diagram because you are not dealing with an ideal gas, in fact, the gas even changes to liquid during part of the cycle. Instead, you have to look up data in steam tables to calculate the efficiency.
10. it's not an ideal gas! instead we need to use steam tables!
11. The working substance in a steam engine is definitely not an ideal gas, so we cannot use the PV diagram. Instead we use the change in enthalpies of the system.

Question 3:

Answer:

1. The atoms that need to be cooled are converted into a dilute gas, and isolated from thermal contact from the surroundings by the proper magnetic fields. The atoms are then bombarded by laser light tuned slightly below the excitation frequency. This means that the only atoms that will absorb the light and emit photons are the ones headed into the incoming laser beam (to the atom, the light is Doppler-shifted to the higher frequency). These atoms will feel a net push backward from the laser light (the emitted photons are in all directions), and this slowing down leads to a lower temp.
2. If you shine a laser at the proper frequency at an atom, the atom will absorb a photon and go to a higher energy state, then spontaneously emit a photon and go back to a lower energy state. Since the laser only comes from one direction and the re-emitted photons are in all directions, the atom feels a force in the direction of the laser. If the frequency of the laser is slightly lower than the one required to excite a transition, only atoms coming towards the laser (which experience Doppler-shifted light) will feel the force.
3. Laser cooling uses the principles of reradiation of photons, the doppler effect, accelerating atoms, and nonuniform magnetic fields. The atom, while traveling towards the laser, feels a force from the laser from the photons hitting it because the reradiated photons are emitted in all directions while the laser light comes from only one direction. The atoms absorb this light in the first place because they are moving, thus the light is doppler shifted back to a wavelength they can absorb. They would not absorb this light at rest. Laser beams coming from up, down, left, right, front, and back will slow all the atoms in a 3-D volume. The applied nonuniform magnetic field then traps the atoms in the center of the chamber, allowing them to cool down to the millikelvin range at least.
4. Six lasers are aimed at the same location and tuned to a frequency that will only be absorbed by atoms moving toward the laser (results from doppler shift). The atoms are pushed backward and slowed down when they absorb photons. Slowing a bunch of atoms cools them down to low temperatures.
5. by hitting a gaseous atom with lasers you can slow its movement to nearly a stop. This effectively takes away all of the kinetic energy that gas atom had, and by removing the kinetic energy, we lower the temperature.
6. The most important principles arer photon absorption and emition. When a laster is fired at an atom it absorbs a photon. Then over a range of time photons are emitted from the atom in every direction. These photon's won't balance the force coming from the laser emitted photons so the atom will feel a net force in the direction of the laser beam. Thus put a bunch of lasers all around the substance in every direction, and when you fire the lasers they all have forces that cancel each other out, and thus any motion by the atom is opposed. And it is darn cold.
7. We shine lasers in many direction at a dilute gas at frequecies slightly less than sufficient excitation enegies. Atoms moving in toward a beam will become excited due to a Doppler shift of the beam. So, it absorbs and emits photons, causing it to lose momentum and enegy, and thus "feeling" force back to it's original position. The cloud of dilute gas slows down because of the lasers and thus cools to a very low temperature.
8. First you need a small cloud of atoms, so that they can't condense. In order to slow the atoms down, which emit excited light isotropically, the laser has to be tuned slightly below the frequency needed to be absorbed by the atom. Moving atoms will then feel a backward force when moving toward the alser, since the process will be doppler shifted. Moving away from the source will not do much, hence by shooting lasers from all sides, you can slow down many atoms.
9. A laser fired onto an atom at a specific frequency will cause the atom to absorb photons and emit photons. The atom absorbs photons from one direction but emits photons in all directions, so it feels a kind of force from the laser. If you decrease the frequency a little, then only atoms moving slightly toward the laser will absorb photons (due to Doppler shift), thus there will be a force pushing photons back. Place lasers in all directions and you can essentially keep the atoms in a gas very still and very cold.
10. A laser fires photos at proper frequencies that retard the motion of atoms causing their kinetic energy to decerease subsequently the temperature to decrease.
11. An atom is hit with a laser, the atom recoils as it gives off a photon, over a whole system, the atoms tend to slow down, lowering the energy, and this cools the object to a avery low temperature.

Question 4:

Answer:

3. When describing the Ottocycle on p. 131 of the book, one of the steps is mentioned in the paragraph as an explosion of vaporized gas and air, which raises the pressure, but not the volume. Does this state of great pressure increase without great volume increase actually exist, or is it a mythical step inserted to help us understand the thermodynamics of the internal combustion engine?
8. none
9. I had a little trouble following the analysis of the steam engine. By the time the text started talking about enthalpy and efficiency, I was lost.
10. it was good.
11. This reading was pretty straightforward.