美国高考培训之SAT2物理选择题的特点及答题方法

　　Five-Choice Completion Questions

　　These are the multiple-choice questions we all know and love, and the lifeblood of any multiplechoice exam. You know the drill: they ask a question, give you five possible answer choices, and you pick the best one. Got it? Good. An example appears below.

　　While you’ll often find two or three questions in a row that deal with the same topic in physics, there is no pattern. You might find a question on modern physics followed by a question on dynamics followed by a question on optics. However, there is a general tendency for the questions to become more difficult as you progress.

　　Five-Choice Completion Question Example

　　Directions: Each of the questions of incomplete statements below is followed by five suggested answers or completions. Select the one that is best in each case and then fill in the corresponding oval on the answer sheet.

　　1. . A gas in a closed container is steadily heated over a period of time. Which of the following statements is true of this process?

　　(A) The average kinetic energy of the gas molecules decreases

　　(B) The mass of the container increases

　　(C) The pressure exerted by the gas on the walls of the container increases

　　(D) The gas changes phase into a liquid

　　(E) The specific heat of the gas decreases

　　Explanation

　　The answer to this question is C. The key lies in remembering the ideal gas law: PV = nRT.

　　According to this formula, an increase in temperature is accompanied by an increase in pressure. A is wrong, since the average kinetic energy of gas molecules corresponds to their temperature: if the temperature increases, so does the average kinetic energy of the molecules.

　　B is wrong because we’re dealing with a closed container: the mass cannot either increase or decrease. D is wrong because a gas must be cooled, not heated, to change phase into a liquid. Finally, E is wrong because the specific heat of any substance is a constant, and not subject to change.

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