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your instrument—the length of the horn, and thus its pitch, varies with the room temperature. Household thermometers also work according to this principle: mercury, a liquid metal, expands when it is heated, and therefore takes up more space and rise in a thermometer. Any given substance will have a coefficient of linear expansion, , and a coefficient of volume expansion, . We can use these coefficients to determine the change in a substance’s length, L, or volume, V, given a certain change in temperature. EXAMPLE A bimetallic strip of steel and brass of length 10 cm, initially at 15ÂºC, is heated to 45ÂºC. What is the difference in length between the two substances after they have been heated? The coefficient of linear expansion for steel is 1.2 10 –5 /CÂº, and the coefficient of linear expansion for brass is 1.9 10 – 5 /CÂº. First, let’s see how much the steel expands: Next, let’s see how much the brass expands: The difference in length is m. Because the brass expands more than the steel, the bimetallic strip will bend a little to compensate for the extra length of the brass. Thermostats work according to this principle: when the temperature reaches a certain point, a bimetallic strip inside the thermostat will bend away from an electric contact, interrupting the signal calling for more heat to be sent into a room or building. Methods of Heat Transfer There are three different ways heat can be transferred from one substance to another or from one place to another. This material is most likely to come up on SAT II Physics as a question on what kind of heat transfer is involved in a certain process. You need only have a qualitative understanding of the three different kinds of heat transfer. Conduction 188
Conduction is the transfer of heat by intermolecular collisions. For example, when you boil water on a stove, you only heat the bottom of the pot. The water molecules at the bottom transfer their kinetic energy to the molecules above them through collisions, and this process continues until all of the water is at thermal equilibrium. Conduction is the most common way of transferring heat between two solids or liquids, or within a single solid or liquid. Conduction is also a common way of transferring heat through gases. Convection While conduction involves molecules passing their kinetic energy to other molecules, convection involves the molecules themselves moving from one place to another. For example, a fan works by displacing hot air with cold air. Convection usually takes place with gases traveling from one place to another. Radiation Molecules can also transform heat into electromagnetic waves, so that heat is transferred not by molecules but by the waves themselves. A familiar example is the microwave oven, which sends microwave radiation into the food, energizing the molecules in the food without those molecules ever making contact with other, hotter molecules. Radiation takes place when the source of heat is some form of electromagnetic wave, such as a microwave or sunlight. The Kinetic Theory of Gases & the Ideal Gas Law We said earlier that temperature is a measure of the kinetic energy of the molecules in a material, but we didn’t elaborate on that remark. Because individual molecules are so small, and because there are so many molecules in most substances, it would be impossible to study their behavior individually. However, if we know the basic rules that govern the behavior of individual molecules, we can make statistical calculations that tell us roughly how a collection of millions of molecules would behave. This, essentially, is what thermal physics is: the study of the macroscopic effects of the microscopic molecules that make up the world of everyday things. The kinetic theory of gases makes the transition between the microscopic world of molecules and the macroscopic world of quantities like temperature and pressure. It starts out with a few basic postulates regarding molecular behavior, and infers how this behavior manifests itself on a macroscopic level. One of the most important results of the kinetic theory is the derivation of the ideal gas law, which not only is very useful and important, it’s also almost certain to be tested on SAT II Physics. The Kinetic Theory of Gases We can summarize the kinetic theory of gases with four basic postulates: 1. Gases are made up of molecules: We can treat molecules as point masses that are perfect spheres. Molecules in a gas are very far apart, so that the space between each individual molecule is many orders of magnitude greater than the diameter of the molecule. 2. Molecules are in constant random motion: There is no general pattern governing either the magnitude or direction of the velocity of the molecules in a gas. At any given time, molecules are moving in many different directions at many different speeds. 3. The movement of molecules is governed by Newton’s Laws: In accordance with Newton’s First Law, each molecule moves in a straight line at a steady velocity, not 189
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SATII PHYSICS (FROM SPARKNOTES.COM)
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The Good • Because SAT II Subject
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Which SAT II Subject Tests to Take
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After grumbling, however, you still
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Waves 15-19% 11-15 Waves 10% 7-8 Op
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negative, so E, and not A, is the c
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including them anyway because it’
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Two positively charged particles, o
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will a visual representation reliev
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Physics Hint 6: Be Flexible Knowing
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There are a number of ways to label
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Adding Parallel Vectors If the vect
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The result of multiplying A by c is
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neither parallel nor perpendicular.
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Suppose the hands on a clock are ve
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Vector Addition Practice Questions
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2. A The vector 2A has a magnitude
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path, Alan has traveled a much grea
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school student called Andrea. Andre
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centimeters to the left of its star
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We can learn two things about the a
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Acceleration vs. Time Graphs After
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The variable represents the object
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Note that there are certain conveni
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1. . An athlete runs four laps of a
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10. . A woman runs 40 m to the nort
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We know the total distance the spri
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Principles of Natural Philosophy. I
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The component form of Newton’s Se
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e in the direction. And since the s
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which reflects its resistance to be
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In the diagram above, the weight an
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A student pushes a box that weighs
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1. . Each of the figures below show
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7. . In the figure above, a person
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Since the block is motionless, the
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When we are told that a person push
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EXAMPLE A water balloon of mass m i
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The graph above plots the force exe
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Though energy is always measured in
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there is a negative amount of work
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smallest. The answer to question 3
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Mechanical Energy Average Power Ins
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to a height of 8 m over a time of 4
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8. C When the book reaches the pers
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determining what those right number
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the ground. The system is initially
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calculators, you almost certainly w
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and minimize M.” With such a ques
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2. WHAT IS THE ACCELERATION OF THE
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Adding these two equations together
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force of friction: . Using Newton
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m, placed on a frictionless surface
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Frequency is given in units of cycl
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of the spring due to the gravitatio
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The oscillation of a pendulum is mu
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Velocity Calculating the velocity o
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Practice Questions 1. . Two masses,
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7. . An object of mass 3 kg is atta
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Since the system is in equilibrium,
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velocity, v. Linear momentum is den
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Conservation of Momentum If we comb
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As we might expect, the final veloc
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A pool player hits the eight ball,
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two-dimensional collision is effect
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For a System of Two Particles For a
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At the front end of the boat, the f
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4. . A scattering experiment is don
Page 137 and 138: 1. B The athlete imparts a certain
Page 139 and 140: 7. E Momentum is conserved in this
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Page 145 and 146: elative position to one another. As
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Page 149 and 150: To find the direction of a rigid bo
Page 151 and 152: A student exerts a force of 50 N on
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Page 159 and 160: Velocity Average Angular Accelerati
Page 161 and 162: 3. . What is the direction of the a
Page 163 and 164: 1. D An object that experiences 120
Page 165 and 166: At the top of the incline, the disk
Page 167 and 168: from a Latin word meaning “center
Page 169 and 170: Newton’s Law of Universal Gravita
Page 171 and 172: when you are beneath the surface of
Page 173 and 174: EXAMPLE A satellite of mass is laun
Page 175 and 176: Kepler’s Laws After poring over t
Page 177 and 178: Practice Questions Questions 1-3 re
Page 179 and 180: 8. . A satellite orbits the Earth a
Page 181 and 182: Circumference and radius are relate
Page 183 and 184: learn how heat is transferred from
Page 185 and 186: heat, like rubber, have a high spec
Page 187: Just as specific heat tells us how
Page 191 and 192: Effectively, this equation tells us
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Page 195 and 196: There are a number of equivalent fo
Page 197 and 198: If we know our formulas, this probl
Page 199 and 200: 5. . An ideal gas is enclosed in a
Page 201 and 202: Asphalt, like most materials, has a
Page 203 and 204: The things we call atoms today are
Page 205 and 206: If they come up on SAT II Physics,
Page 207 and 208: will move in the opposite direction
Page 209 and 210: Work The work done to move a charge
Page 211 and 212: Much like gravitational potential e
Page 213 and 214: 3. . A particle of charge +2q exert
Page 215 and 216: 7. . A particle of charge +q is a d
Page 217 and 218: The vector sum of the three vectors
Page 219 and 220: Voltage The batteries we use in fla
Page 221 and 222: This equation tells us that we can
Page 223 and 224: If the two variables you know are a
Page 225 and 226: However, each resistor causes a vol
Page 227 and 228: So = 4 . WHAT IS THE CURRENT RUNNIN
Page 229 and 230: Consider again the circuit whose to
Page 231 and 232: This circuit consists of resistors
Page 233 and 234: The junction rule deals with “jun
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The Greek letter is called the diel
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4. . Two resistors, and , are ident
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10. . A dielectric is inserted into
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The equivalent capacitance of two c
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The Earth itself acts like a huge b
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Because the velocity vector and the
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A particle with a positive charge o
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The constant is called the permeabi
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1. . The pointer on a compass is th
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7. . A positively charged particle
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1. B To solve this problem, it is h
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If the particle is to move at a con
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flowing in the counterclockwise dir
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Next, let’s calculate the flux th
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Remember that field lines come out
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Magnetic Flux Faraday’s Law / Len
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5. . A wire carrying 5.0 V is appli
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In this equation, A is the amplitud
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Ernst attaches a stretched string t
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A string is tied to a pole at one e
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other. The principle of superpositi
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Nodes The crests and troughs of a s
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The Doppler Effect So far we have o
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Practice Questions 1. . Which of th
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6. . Two pulses travel along a stri
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1. B Simple harmonic motion is defi
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where and are the frequency heard b
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A higher frequency—and thus a sho
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The phenomenon of refraction result
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Since we know that the ratio of / i
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The four basic kinds of optical ins
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You can test all this yourself with
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Because is a positive number, we kn
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As the diagram shows us, and as the
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At any point P on the back screen,
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Note that the pattern is brightest
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One of the more common ways of test
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3. . When the orange light passes f
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9. . Sound waves do not exhibit pol
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7. E Only concave mirrors and conve
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For people who believed that light
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What does this all mean? Time is re
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A spaceship flying toward the Earth
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Rutherford’s Gold Foil Experiment
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The Wave Theory of Electromagnetic
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The Problem with Rutherford’s Mod
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Don’t worry: you don’t need to
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A hydrogen atom is energized so tha
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where is the uncertainty in a parti
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electrons have mass, it is so negli
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chapters on mechanics are the resul
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You won’t need to calculate the n
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Photoelectro n Radius of Electron O
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5. . An electron is accelerated thr
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according to the formula , where l
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In radioactive substances, the numb
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A scale for measuring temperature,
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The points of maximum displacement
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Electromagnetic spectrum The spectr
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The amount of time it takes for one
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Given the period, T, and semimajor
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The substance that is displaced as
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A back-and-forth movement about an
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Refracted ray Refraction Restoring
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T Tail Tangent A body or set of bod
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Weber Weight The force involved in
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pinpointing what you need to study
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If you got a question wrong because
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