Reading Quiz

Question 1:

Answer:

1. I'm okay for now.
2. nothing in particular
3. Nothing at this time.
4. None :)
5. Nothing from class, but in the book they talk about tank circuits, and I don't quite understand how they work.
6. none
7. nothing
8. I think I'm still caught up.
9. Everything I had questions on has been been clarified through class, thanks.
10. I was confused about electromagnetic waves.
11. I think I understand most of the material from wednesday's class
13. 2,450,000,000 Hertz
14. i am still a little sketchy about the band gaps and all of that stuff
15. none, thanks
16. None.
17. --
18. I think I pretty much get everything so far.
19. I am still confused about the idea of polarization of waves.
20. none
21. graphing the waves of binary (the lab on monday)

Question 2:

Answer:

1. The electromagnetic radiation used in a microwave has a frequency of 2.45 GHz (or 2.45 x 10^9 Hz) because it cooks food uniformly.
2. The frequency is around 2.45 GHz.
3. 88MHz-108MHz
4. 300 MHz to 300 GHz
5. 2.45 GHz
6. 2.45-GHz
7. the frequency of the microwaves range from 300 MHz to 300GHz
8. 2.45GHz if I understood this section properly.
9. 2.45 GHz
10. 10^10 Hz
11. A microwave uses waves witha a frequency of 2.45 gigahertz. (2,450,000,000Hz)
12. 2.45 GHZ
13. The microwaves cause polarized water molecules to rotate back and forth, which causes thermal energy from the molecules bumping into eachother. Ice has a complex crystaline structure unlike water, and it constrains the water molecules from knocking into eachother.
14. 2,450,000,000 Hertz
15. 2.45 Ghz
16. On the scale in the picture it says 10^10 Hz, but the note to the side says from 300 MHz to 300 GHz, which corresponds with the different possible wavelengths.
17. 2,450,000,000 Hz
18. Around 10e10 or 10e11 Hertz
19. The frequency of the mocrowaves are 2.45-gigahertz (2,450,000,000-Hz).
20. from 3 x 10^8 Hz to 3Hz.
21. the frequency ranges from 300 MHz to 300 GHz

Question 3:

Answer:

1. A microwave is efficient in heating liquid water but it doesn't work as well on ice because the microwaves cause the water molecules to twist back and forth to create the heat. The tightly packed crystal structure of ice does not allow the water molecules to turn easily. Since the molecules can't turn, no heat is generated, therefore the ice does not heat up and melt.
2. Liquid water is made up of water molecules, which are slightly polarized because of their shape. They have a positive and a negative side, and when the electromagnetic waves in the microwave hit them, they keep trying to align themselves to the field. All of this moving causes friction and thermal energy, causing the water to heat up. Ice, however, is in a solid form, so the water molecules are more stuck in place and aren't free to rotate around to align with the field, so they dont heat up.
3. Ice-Polar water molecules are aranged in an orderly fashion with fixed positions and orientations. Water, on the other hand, molecules are more randomly oriented.
4. Water molecules in liquid form are able to rotate in alignment with a field more easily, while ice molecules are more strongly bound to each other and do not allow microwave to flow through them.
5. The water molecules in ice are held in a rigid structure, while the molecules in liquid water are free to move around, so they can turn and collide, eventually heating up.
6. The microwave heats food by rapidly twisting the water molecules back and forth. Water molecules are free and polarized and twist well, but ice doesn't heat well in a microwave because the water is frozen in a rigid structure and the molecules can't twist freely.
7. In ice, the polar molecules are arranged in fixed postions and orientations so they cant move very easily to align with the electric field. With liquid water, the molecules are more randomly orientated and will rotate to align with the elcetric field. Because they are so close together, when the molecules move they hit each other which causes heat.
8. The heat produced comes from turning the molucules in water or other foods containing water. In ice the molecules are basically crystalized so they are unable to move freely enough to generate much heat.
9. In liquid water, the molecules are more free to experience a torque created by the molecule rotating into alignment with the electric field. The rotation of the molecule causes it to bump into other molecules, resulting in the conversion of electrostatic potiential energy to thermal energy. The crystal structure of ice prevents the water molecules from turning easily.
10. A microwave oven efficiently heats up liquid water but not ice because portions of food that defrost first absorb most of the microwave power and overheat while the rest of the food remains frozen solid.
11. In liquid water the molecules are fairly free to rotate back and forth, and when they do this they bump one antoher and encounter friction and thus create heat. In ice, the molecules cannot move around, they are locked in one position, so they cannot rub one another and create heat as in liquid water.
12. the microwaves excite the molecules in liquid water, causing them to vibrate extremely quickly, which produces friction and thus heat. However, in ice, the structure of the ice crystal prevents the water molecules from moving as much, so they cannot produce as much friction.
13. Its bad to wrap food in metal like tin foil because the metal reflects the microwaves and your food won't get warm. It is also bad to put sharp metal objects in the microwave because the accumulation of charge can cause a spark and fire could start.
14. The microwaves cause polarized water molecules to rotate back and forth, which causes thermal energy from the molecules bumping into eachother. Ice has a complex crystaline structure unlike water, and it constrains the water molecules from knocking into eachother.
15. Water molecules start spinning in the direction of an electric field that they are exposed to because they are polar molecules, as they spin they hit each other resulting in thermal energy being released. This does not work with ice because the molecules are arranged in a rigid structure as opposed to the fluid structure of water.
16. The polar, unaligned molecules of liquid water will rotate into alignment when placed in a strong electric field, like a microwave. As they do so, molecules will hit each other, converting some potential energy into thermal energy. At the same time, the water absorbs the microwaves, converting THEIR energy into thermal energy as well. It is not just liquid water, then, but molecules with such a random orientation that are easily heated by microwaves. In ice, the polar molar molecules are fixed, in an orderly alignment. Since these frozen water molecules cannot turn easily as they can in liquid water, they can't easily turn and bump each other to convert potential energy into to thermal energy.
17. Water molecules in the liquid are free to rotate whichever direction the changing electric field from the microwave wants them to because of their polarization. Ice has a crystal structure so there is more holding the molecules in place and keeping them from turning and running into each other.
18. Because a microwave's fluctuating electric field twists the water molecules back and forth billions of times per second and as the molecules turn, they bump into one another and heat up. Ice, however, has trouble doing this being of its crystal structure which doesn't allow the water molecules to move around and turn as freely.
19. Because of the crystal structure of ice, the water molecules are constrained and cannot freely twist back and forth in order to heat up. In liquid water, the water molecules are free to turn back and forth and bump into each other and heat up.
20. Water works well because their molecules move around as the microwave's electric field fluctuates. Water absorbs the microwaves and converts their energy into thermal energy. But microwave power does not work well with ice because the ice's crystal structure contrains the water molecules to they can't turn easily.
21. because in ice the polar water molecules are arranged in an orderly fashion with fixed positions and orientations while in liqid water the molecules are more randomly oriented

Question 4:

Answer:

1. It is bad to put any thin metal in the microwave, and it also is bad to put any sharp metal in. Thin metal has high resistance and therefore will quickly overheat, and sharp metal will collect charge on its tip, and then some will jump into the air as a spark.
2. It is bad to put metal in the microwave when the metal object has a sharp point or when it is thin and not a good conductor.
3. One can cook food in a shallow metal dish, however you should never put a sharp metal objet in the mircrowave becaue of risk of starting a fire.
4. When microwaves push charge back and forth in a metal, the metal experiences an alternating current, which experiences a voltage drop and heats up the metal causing it to overheat
5. It's bad to put sharp pointed metal objects, since they can lead to sparks. Aluminum foil will reflect the microwaves and the food won't cook.
6. It's extremely dangerous to put metal that is thin and poorly conducting and/or has sharp points in a microwave, especially when something flammable is in the microwave because the metal will cause sparking.
7. It is bad to put metal in a microwave if the object is pointy because it may cause a spark and ultimately a fire. It is also bad to put thin strips of metal in a microwave because they overheat quickly.
8. Its bad when the metal covers the food you're trying to cook because then the microwaves just bounce off the metal and dont heat up the food. Also, its bad if the charges build up on the sharp tip of the metal because that can cause sparks which can in turn cause fires.
9. When the metal has sharp points (can create sparks) or is a poor conductor of electricity (tends to overheat and catch fire to flammable objects)
10. It is bad to put a sharp metal object in the microwave because it can cause a spark and cause a fire.
11. If metal is thin and doesnt conduct electricit well, it can overheat very rapidly in a microwave. Also if enough charge is pushed into a sharp point of metal, some of it will jump into the air as a spark, and this can cause a fire.
12. something metal with a sharp point is bad to put in the microwave. Charge from the microwaves can accumulate at the point and cause a spark. Also, thin strips of metal are bad, as they can overheat and cause a fire.
13. I would like to go over magnetrons
14. Its bad to wrap food in metal like tin foil because the metal reflects the microwaves and your food won't get warm. It is also bad to put sharp metal objects in the microwave because the accumulation of charge can cause a spark and fire could start.
15. It is bad when it is surrounding the food you are cooking because it will reflect the microwaves and your food will not cook. Sharp metal objects are bad because they can build up enough charge to emit a spark which can potentially start a fire. Also thin pieces of metal might not conduct the electricity well enough so they will overheat and can melt.
16. If there is enough charge on the pointy end of an object such as a twist tie or a scrap of aluminum foil, some of this charge will jump into the air as a spark, which can start a fire. This makes sense with what we learned about corona discharge and how charge concentrates on a pointy end.
17. When the metal has a sharp edge because too much charge to be distributed to a very small area of the metal.
18. If you wrap food in aluminum foil, the foil will reflect the microwaves and the food won't cook and sometimes with a sharp piece of aluminum foil, charge will be pushed onto a sharp point on the foil. If enough charge accumulates, it will jump into the air and create a spark, which could potentially start a fire especially if the foil is attached to something flammable.
19. If you put a sharp metal object in the microwave, this can be very dangerous because the charge concentrates at the sharp point and can jump into the air as a spark which could start a fire.
20. When the metal has a sharp point that charge is pushed to, such as a scrap of aluminum foil or a twist-tie, then a spark can erupt, which can cause a fire in the microwave.
21. if the metal has a sharp point that might spark and cause a fire

Question 5:

Answer:

1. I feel that I understood this section -- I found it really interesting because I never though about how microwaves work!
2. I got a little lost when it explained how only the combination of electric and magnetic fields will work.
3. I'm confused with how a magnetron works in the microwave.
4. None
5. Where is the small antenna in the microwave oven that produces the microwaves?
6. everything was pretty clear. It would be interesting to see what a magnetron looks like.
7. The section about the magntron was confusing. I don't understand how it works at all.
8. Still got it.
9. How a magnetron works.
10. I did not have any trouble with any concepts in this reading.
11. I think I understand the topics covered in this reading
12. how a magnetron works and especially how it produces microwaves from electric current and a magnet.
13. I would like to go over magnetrons
14. None, thanks
15. I'm not sure about check your understanding #1: microwave popcorn. I'd also like to spend time discussing the section about creating microwaves with a magnetron further.
16. --
17. I think I understood everything in the reading.
18. I was confused about the details in how a magnetron works.
19. none
20. ice and water in a microwave -- why do they react differently