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Physics at the Community College

OK, to follow is the review for my comprehensive final exam in second-semester college physics. But first, a little background.

This is the SAME CLASS that I took at Oak Ridge High School in 1983 or so. ORHS is a wonderful school that offers a great deal to the college-bound student, including a great variety of Advanced Placement classes which are specifically designed to help you test out of first-year college classes. I took full advantage of the AP classes and tested out of an entire year of college, which gave me plenty of room to explore all my interests once I got there. I ended up with a double major in Holistic Health (chosen) and Philosophy (accidental).

I am re-taking physics because it is perceived to be difficult, and I want to prove to the admissions staff at NCNM and other schools that I am still academically viable. They consider credits to be expired after seven years, and many of my credits are extinct. So I am re-taking some of the prerequisites for entry into Naturopathic Medicine programs. This physics class is a two semester class with labs, based on algebra---not calculus. If you ask a physicist, they will tell you that these problems are much easier to solve using calculus. Perhaps it is true. I wouldn't know. I took one semester of calculus about seven years ago and never used it for anything. It's gone now.

In the previous semester of physics I had a superior teacher and learned a LOT. Unfortunately for me, he got a full time job teaching science at Flagstaff High School, and those kids are lucky to have him. This semester has been an exercise in jumping through hoops, and I am eager for it to be over. This review, should you take the time to read it, will give you an idea of the level of the class. Frankly I thought it was way too easy, that the teacher glossed over the subject matter and avoided the difficult parts because she didn't understand them well enough to teach them. Most of the people in this class were psyched that it was easy. They don't care to learn physics, they just want a grade. I was disappointed. Here she is feeding us the final: the exam will be JUST LIKE this review. She will give the exact same problems with different numbers. She will have multiple guess "concept questions" based on this review.... I learned more physics in high school.

On to the last few hoops. This review is worth 40 points if turned in.

CH13 Temperature and Kinetic Theory
1. Temperature is a measure of the kinetic energy of particles or molecules.
2. To compare the three temperature scales, Kelvin is the scientific scale, with zero being based on absolute zero, a theoretical condition of molecules having no kinetic energy. The size of a degree in Kelvin is the same as Celsius, making them easy to convert. Celsius' zero is the freezing point of water, and boiling is 100 degrees, so freezing in Kelvin is 273 and boiling is 373. Fahrenheit is the scale used by the fewest people, with oddball numbers for no obvious reason. Freezing water happens at 32 and boiling at 212.
3. The Ideal Gas Law is PV=nRT, where P is pressure, V is volume, n is mols of gas, R is a constant (8.314 Joules/mol x K), and T is temperature. Variables that are directly proportional to each other are T and P, also T and V. Inversely proportional are P and V.
4. Identify on a phase digram: melting point, boiling point, triple point, and critical point. Melting and boiling points are not points but lines, the lines that divide the phases on the graph. Triple point is where the three lines come together. Critical point is the very high temperature end of the line dividing liquid and gas, at which the liquid and gas are no longer distinguishable from each other. For water this happens at 647K.
5. Convert 68 degrees F to Celsius. Degrees C = 5/9 (degrees F-32), so answer is 20 degrees C
6. What is the volume of 661 moles nitrogen gas at STP? STP is standard temp and pressure, or 20 C and 1 atmosphere. Rearrange the Ideal Gas Law and get V = nRT/P so V is (661 mol)(8.314 J/mol x K)(293 K) / 100000 Pa = 16 meters cubed. OK so now I have established that it's a bother trying to represent the problems in text here, so I'm going to do them on paper separately.
7. What is the velocity of molecules inside a helium-filled chamber that contains 6.64 x 10 to the -27 kg of gas, at a temp of 6,000K? Answer: 6116 m/s. They're moving! See green paper.

CH14 Heat
8. A change in phase requires energy, but the temperature does not alter during the phase change.
9. Heat of Fusion is the energy required melt 1 kg of solid to the liquid phase. Heat of Vaporization is the energy required to change 1 kg of liquid to vapor.
10. Specific Heat is the amount of heat energy required to raise the temperature of a specific quantity of a substance by certain amount. The commonly given example is water, which has a specific heat of 1.00 in its liquid phase because it takes one calorie to increase the temperature of 1 gram of water by 1 K. Calories with a capital C are used for measuring the energy stored in food, kilo meaning 10 to the 3rd, so one Calorie is 1000 calories. One calorie has a mechanical equivalent of 4.186 Joules (unit of work).
11. Conduction is the exchange of heat energy by direct contact, and more specifically by molecular collision. Convection is heat transfer by the movement of a flowing mass, such as air or water. Radiation is the transfer of heat energy by electomagnetic waves, without a medium, such as the radiant energy of the sun.
12. A 35 gram glass thermometer reads 21.6 C before it is placed in 135 mL of water. When the water and thermometer come to equilibrium, the thermometer reads 39.2 C. What was the original temperature of the water? mc change in T (glass) = mc change in T (water). Answer: 40.1 C

CH15 Thermodynamics
13. The Law of Conservation of Energy is the first law of thermodynamics, and says that energy is not created or destroyed, it merely changes forms. In lecture we were taught that "you can't get more heat out than goes in". Another way of stating it is that an increase in the energy of a system equals the amount of energy added--minus the work done by the system on the surrounding environment. The two main forms of energy are potential and kinetic.
14. The first law of thermodynamics is the conservation of energy. The second law is ENTROPY, which is the idea that any spontaneous process involves an increase in entropy, and generally a decrease in order. To create order requires an input of energy. You can't unsmash a coffee cup.
15. The electrical energy resources lists on page 431 include fossil fuels, nuclear, hydroelectric, geothermal, wind and solar. The question is which ones are sustainable, and which are economically viable. Fossil fuels: not sustainable, economically viable only while supplies last. Nuclear: sustainable if we are able to maintain the infrastructure when we run out of oil, very expensive startup costs but will become more economically viable as fossil fuels are depleted. Hydroelectric: sustainable and viable, the cost is damming up our rivers. Geothermal: sustainable as long as nobody messes up the earth's crust in your neighborhood, viable if you can access it but expensive to startup if you don't have a hotsprings in your back yard. Wind and solar: sustainable and viable after startup costs, depending on location.

CH16 Electric Charge
16. The charge of electrons is negative, neutrons are neutral, and protons are positive. The amount of charge on the electron and proton is - or + 1.6 x 10 to the -19 Coulombs. The mass of an electron is 9.11 x 10 to the -31 kg. The mass of the proton and neutron are 1.67 x 10 to the -27 kg.
17. The coulomb is the unit of charge. It takes 6.25 x 10 to the 18th electrons OR protons to make up 1 coulomb of charge.
18. Three ways to charge an electroscope are permanent and temporary induction, and conduction. The residual charge on the electroscope after each method is as follows: temporary induction--no charge, permanent induction--opposite from charge of inducer, conduction--same as charge of contacting conductive substance.
19. An electric field is considered to be pointed in the direction that a positive test charge would move if dropped into the field. The arrows when such a field is drawn go toward the negative and away from the positive.
20. Find the distance between two equal and opposite charges, each having a charge equal to 111 protons, if the electric force between them is 2.0 x 10 to the -28 Newtons. Answer: 119 meters. Q proton = 1.6 x 10 to the -19 coulombs. k is a constant. F = kQ1Q2/distance squared. See green paper.
21. Consider an equilateral triangle with a perimeter distance of 228.93 km (which means a side is 76.31 km and each angle is 120 degrees). Suppose three charges are placed at the vertices of the triangle: Q1 = 8.8 nC (nano = ten to the -9th) at the bottom left vertex, Q2 = -2.4nC bottom right, Q3 = 4.0nC top vertex. Find the resultant electric force acting on Q1. (This is a longer version of the preceding question and will also be done on the green paper). Steps to complete: calculate charges between point charges, split angled force into vertical and horizontal force vectors and calculate net forces on Q1, find resultant vector force and angle from the vector triangle. See green paper.

CH18 Electric Currents
22. Electric potential energy is work stored against an electron's tendency to move toward the positive plate (in a battery). Potential difference is work done per unit charge in volts, and is measured in Joules. Voltage = Joules / Coulombs. Batteries are devices for chemically storing potential energy that can be released as electricity. Batteries are made of a positive and negative plate, connected by a pathway for electrons to move between the two charged plates.
23. Current is charge flowing (in a wire usually) per unit time, and is measured in amperes. Amps = Coulombs/second. An ammeter is used to measure amps, and is placed in series with the circuit and has low resistance. Resistance is opposition to the flow of electrons, and is measured in ohms. Resistance = voltage / current or R = V/I (Ohm's law). Resistance is measured by using a volt meter which is wired in parallel to the circuit and has high resistance. Knowing the voltage and amperage you can calculate the resistance using Ohm's law.
24. Ohm's law: V = IR, so as either resistance or current increases, with the other remaining the same, voltage must increase. Voltage is directly proportional to both current and resistant. Current and resistance are inversely proportional to each other.
25. Be able to identify and draw the common schematic diagram symbols. Review on green paper: capacitor, ground, fuse, ammeter, volt meter, resistor, battery, current direction, variable resistor.
26. Energy is the ability to do work and is a scalar quantity. Potential and kinetic are common forms of energy. Power is the amount of work done per unit time, measures in watts.
27. An ammeter is wired in series with a circuit and has low resistance, so the current flows through it. A voltmeter is wired in parallel with the circuit and has a very high resistance.
28. A hairdryer has 50 ohms resistance and draws 3 amps of current. a) how much power does it use? use P = IV b) if the dryer is used for 10 minutes, how much energy does it use? A Watt is a Joule/second, so convert to Joules and ten minutes. c) at $.85/kWh, how much does it cost to operate the dryer? Multiply $.84 x 1/6 hour x .450 kWatts = $.064. See green paper for work.
29. See Green paper. Calculate current given voltage and resistance, you get 5.63 amps. Amps are coulombs per second, and one electron has a charge of -1.6 x 10 to the -19th coulombs, so you can figure out how many electrons based on amperage. See green.
30. See Green paper. This is a problem we did for homework using P = IV then E = mc x change in T = Pt and solve for t.
31. In a series circuit, the total resistance is equal to the sum of all resistors on the circuit. The current remains constant throughout the circuit. The total voltage is a sum of all the voltages in a series circuit. All these quantities are related by V = IR at every point in the circuit. As resistance increases in a series circuit, the current decreases.
32. In parallel circuits, the current splits at each split in the wiring, and joins back up when the wires do, just like a river going around islands. The voltage remains the same on either side of the island. The rule for resistors is that the inverse of the total resistance is equal to the sum of the inverses of each of the parallel resistances.
33. See Circuit chart (stapled on). Distribute amps first, then use V=IR to solve for all you can, then solve for volts, then V=IR again, and you're there.

CH20 Magnetism
34. Electric currents produce magnetic fields. Magnetism of a solid is caused by the alignment of molecules as they are solidifying from a liquid such that more of one charge (+ or -) is exposed to the outside world at one end of the object. This can happen when the solid is formed from a liquid in the presence of an already existing magnetic field. The unit for measuring the strength of a magnetic field is the Tesla.
35. Magnetic field lines are drawn radiating out of the north pole of the magnet, and into the south pole.
36. The north pole of the earth is the south pole magnetically, so it isn't "like" a magnet, it IS a magnet.
37. The aurora borealis is caused by charged particles getting captured in the earth's magnetic field, and tracking along the field lines.
38. A moving electric charge induces a magnetic field that is perpendicular to the direction of the current and perpendicular to the direction of the force as well. The right hand rule gives a simple way to remember the direction of the magnetic field lines. Grasping the wire with your right hand, orient your thumb such that it points in the direction of the current. Your fingers automatically encircle the wire in the direction of the magnetic field.
39. How much current is flowing in a wire 4.8 m long if the force on it is .75 N when placed in a .80T magnetic field? Use F = I x length x B where F = .75N, I = ?, length = 4.8 m, and B = .80T. See green.
40. A .12m long solenoid has 420 turns of wire and carries 2.0 amps current. Calculate the magnetic field within the solenoid. Use B = constant x I x N / length. N is the number of turns.

CH21 Electromagnetic Induction
41. Inducing an electromotive force causes electrons to move along a wire. Current can be induced by moving a magnet in a coil. The maximum magnetic field occurs when the movement is perpendicular to the wire. An "induced emf" is the force created by the field made by moving a magnet in a coil.
42. A generator is a device for converting mechanical energy to electrical current. An electric motor is a device that converts electrical energy to mechanical energy. They are related by the fact that they convert between the same two energy states, just in opposite directions.
43. A transformer increases or decreases an ac voltage. A step up transformer increases the voltage for transmission, while a step down transformer decreases voltages for household use.
44. Diameter of coil = 10.2cm. Perpendicular to B = .63T. Time span = .15 seconds. "the field is changed to one of .25 T parallel to the wire coil. What is the average induced emf in the coil?" See green.
45. A transformer is designed to change 120 V into 10,000 V, and there are 164 turns in the primary coil. How many turns in the secondary coil? Vs/Vp = Ns/Np...see green.

CH22 Electromagnetic Waves
46. Electromagnetic waves are self propagating and have electric and magnetic components. The magnetic and electrical field waves are perpendicular to each other and to the directoin of wave motion. EM waves are classified by frequency (see #48).
47. The speed of light in a vacuum is 3.00 x 10 to the 8th meters/second. The meter is based on how far light travels in a second.
48. The lowest frequency EM waves are radio waves, moving up in frequency we have microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays finally the highest frequency radiation: gamma rays. Radio waves can be generated and detected by electronic means. Carrier waves are modified to be FM (frequency modulated) of AM (amplitude modulated). A good antenna for picking up radio waves is close to 1/4 of the wavelength of the carrier wave. Microwaves match the spacing inside a water molecule and the molecules resonate with the wave when exposed. This heats your food and cooks birds that sit on microwave towers. Infrared radiation is heat energy, and many mammalian predators have eyes that can see this frequency. Visible light is visible to humans, and the lowest frequency is red, moving through orange, yellow, green and blue to violet, the highest frequency. The wavelengths of visible light range from 4,500-7,500 Angstroms. An angstrom is 10 to the -10 meters. Ultraviolet radiation is more energetic and harmful. We get it from the sun, and the ozone layer used to block it but now we get skin cancer instead. X-rays are higher energy yet, and travel through soft tissue but are reflected from bones and teeth. The Phoenix airport is the first in the US that is x-raying all passengers without our consent. Gamma rays are the very high frequency radiation given off by radioactive materials such as uranium, and nuclear explosions. These rays rip through cells and destroy them. The only thing that will stop them is a large mass of high density material, such as a thick wall of lead, or a thicker wall of concrete.
49. Olaus Roemer measured the speed of light by watching a moon of Jupiter known as Io. He measured the period of the moon which appeared to take longer at certain times of the earth year than at others. What he was observing was the difference in when the light arrived based on the motion of the earth relative to Jupiter's system. He calculated a speed of light of 2.2 x 10 to the 8th m/s, which is not too shabby.
50. Albert Michelson measured the speed of light more accurately using late 1800's technology, and got a Nobel Price for it in 1907. Michelson's experiment involved a rotating 8-sided mirror, and bouncing light off a mirror in the distance. With the 8-sided device rotating, he was able to get it moving so fast that a constant beam of light was transmitted from his source to the 8-sided, to the distant mirror, to the 8-sided and out to a viewer's eye. Then by measuring the speed of rotations on the 8-sided thing he could deduce the speed of light.
51. AM and FM waves are broadcast by modifying a carrier wave. AM waves have variable amplitude, FM waves have variable frequency. Both are induced by running alternating current in an antenna based on a specific set of data, for example music, which creates the wave in space. That wave is received by an antenna of the right length and a receiver demodulates the signal to get at the original information.
52. A rotating mirror is placed 35 km (d = 70km) from a reflecting mirror; at what frequency must the mirror rotate to "match" the speed of light? (536Hz). First use d = vt then assuming the mirror is 8-sided, use f = 1/8t. See green.
53. What's the lag in hours of light coming from Pluto at a distance of 5.91 x 10 to the 12th meters? See green. A simple conversion where you divide the distance in meters by the speed of light in meters per second, then convert seconds to hours. (5.47 hours)
54. Walkie talkies using 900 M Hz frequency have range of 60m. (Mega is 10 to the 6th) How many wavelengths can fit between your ear and another talker 60 m away? (180 wavelengths) See Green. Find wavelength then divide distance by wavelength.

CH23 Geometric Optics
55. A real image can be projected onto a screen, and is always inverted. A virtual image cannnot be projected, is erect, and appears to be behind the lens or mirror.
56. The focal point is half of the distance of curvature away from a spherical lense or mirror.
57. A plane mirror forms an image the same size as the object, virtual, with right and left reversed.
58. To follow is a listing of what kinds of images will be formed by a concave mirror with an object placed at a range of distances.
Object at infinity (like the sun) form an image at the focal point that is reduced and real, and inverted, though it is so small you can't tell that.
Object at a finite distance forms an image that is reduced, inverted, real, and located between f and r.
Object at the (anti) radius of curvature forms a real, inverted image the same size as the object and at the same location.
Object between the (anti) radius of curvature and the (anti) focal point forms an inverted, real image that is magnified and located beyond r.
Object at the (anti) focal point forms no image.
Object within the (anti) focal point forms a virtual image behind mirror that is magnified and erect.
59. Convex mirrors form virtual images.
60. Ray diagram review.
61. The index of refraction is a constant for a medium that indicates how much light will bend when passing into that medium. It is dependent on the density of the medium. Index of refraction n is obtained by dividing the speed of light in a vacuum by the speed of light in the medium for which the index is sought. n = c / v.
62. Total internal reflection occurs when the light is shining from a more dense medium to a less dense medium, and exceeds the critical angle so that no light escapes. The incident angle is greater than the critical angle.
63. A ray refracts toward the normal when traveling from a less dense medium to a more dense one. When the same light is travelling into a less dense medium it refracts away from the normal, and when the incident angle is 90 degrees the light does not refract.
64. Rays bend when transitioning between mediums of different densities because the light moves at different speeds, and the wave's wavelength increases or decreases. Frequency remains constant.
65. To follow is a listing of what kinds of images will be formed by a convex lense with an object placed at a range of distances.
Object at infinity (like the sun) form an image at the focal point that is real and inverted.
Object at a finite distance forms an image between f and r that is real, reduced, and inverted.
Object at the (anti) radius of curvature forms an image at r that is inverted, real, and the same size as the object.
Object between the (anti) radius of curvature and the (anti) focal point forms an image beyond r that is inverted, real, and enlarged.
Object at the (anti) focal point forms no image.
Object within the (anti) focal point forms a virtual image that is magnified and upright and between f and r.
66. Ray diagram review.
67. Sign conventions: di and do if positive indicate a real image, if negative then virtual. If f is positive the mirror is concave, if f is negative, convex. If m is positive the image is erect, and if it is negative the image is inverted.
68. A concave mirror has focal length of 35 cm. Object is 20 cm tall. Object distance is 45 cm. What is image distance and image height? use 1/di = 1/f - 1/do, then hi/ho = di/do.... See Green.
69. Hummingbird egg question. See blue pages! First find di which = -m x do. Then use 1/f = 1/di + 1/do to find f.
70. A ray of light travels from air into water (n = 1.33) at 42 degree angle, at what angle is this ray refracted within the water? See blue. Plug & chug.
71. What is the wavelength, in water, of blue light whose wavelength is 450 nm in air? See blue pages. First find f then find v in water using known n of 1.33.

CH24 The Wave Nature of Light
72. Huygen's principle is that each point in an advancing wave front is in fact a new wave-creating disturbance, ie. waves are self-propagating.
73. Diffraction is the bending of light around an object, and refraction is the bending of light as it passes from one medium to another.
74. Young's double slit experiment results in light and dark bands on a screen because of interference of the waves of light. Where the light interferes destructively, no light is seen on the screen, and where the interference is constructive, you'll see a bright spot.
75. A diffraction grating is a plate with many very fine parallel and equally spaced grooves in it. This arrangment diffracts light and causes interference between the beams of light coming through each slit. The sizing of the grooves should match the wavelength of the light it is intended to study. The function of a diffraction grating is to separate a polychromatic beam of light into its consituent wavelengths, ie. it is "dispersive".
76. The alternating light and dark lines between my fingers when I peer between them at a light source is caused by the diffraction of the light around my fingers, and the interference of the light waves as they come through the narrow slit.
77. Light question, double slit equation, given: wavelength = 5.3 x 10 to the 7th, x (dist of 1st order line from center) = 25 cm, n = 1. Question appears to be mis-written. Need either L to solve for d, or d to solve for L. See blue.
78. At what angle will 560 nm light produce a 22nd order light band when falling on a diffraction grating whoese slits are 1.45 x 10 to the -3 cm apart? See blue.

CH25 Optical Instruments
79. And eye is like a camera because they both have an iris, lense and shutter. The blind spot of the eye is not found in a camera.
80. For nearsightedness one uses a diverging lense, and for farsightedness, a converging lense.
81. A refracting telescope uses lenses, and is only useful at a relatively small size because of the chromatic and spherical aberrations that appears due to the lens, and because you can only support the big lens around the sides. The reflecting telescope is more commonly used by modern scientists because you can build it large scale using mirrors supported from underneath eliminating the design constraint of the lense as well as the aberrations.
82. A CT scanner (aka CAT scan used for medical imaging) uses a series of xrays taken on the same axis of some part of the body to compile a 3 dimensional image of the internal contents.
83. The numbers on a binocular refer to the magnification (the first and smaller number) and the diameter of the objective lens (the second and larger number).
84. An endoscope uses the same principles as a periscope to see inside the cavities of the human body.


( 2 comments — Leave a comment )
Dec. 9th, 2006 06:15 pm (UTC)
Nice review. Even I could do those problems with little effort, and I am science-phobic. Aren't you just fed up with HAVING to take these high school classes?? I know I am.
Dec. 9th, 2006 10:34 pm (UTC)
Yes, I am fed up. I would love to take some classes there were about what I care about, and taught to me at my level. Wouldn't that be nice?
( 2 comments — Leave a comment )



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