Backward Reasoning Approach in Exposition Questions
Utilize backward reasoning in exposition questions to underline subject matter, apply relevant physics knowledge, and deduce judgments. This strategy involves analyzing scenarios like heat transfer in making frothy milk to arrive at accurate conclusions. Through tackling questions step by step, you'll enhance your problem-solving skills and critical thinking abilities.
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Attacking Exposition Questions Backward Reasoning Approach 1. Underline the subject matter to make judgment on; 2. select the relevant Physics knowledge involving the subject matter in this context (usually this knowledge would have been applied in earlier parts of the question); 3. apply the knowledge to the condition in the question to arrive at a judgment. Concepts, laws, equations, etc 2
Exposition : attacking strategy (Source: 2012 DSE 1B Q1c) Cappuccino is an Italian style coffee topped with a layer of frothy milk (Figure 1.1). Figure 1.1 Frothy milk is made by bubbling steam through milk, which is held in a metallic jug (Figure 1.2). Steam is ejected from the steam wand of a cappuccino machine (Figure 1.3). Figure 1.3 Figure 1.2 3
Exposition : attacking strategy (a) Calculate the total amount of heat released when 20 g of steam at 110 C cools to 100 C and condenses to water at 100 C. (b) 20 g of steam at 110 C is bubbled through 200 g of milk at 15 C to make frothy milk. Using the result in (a), estimate the temperature of the frothy milk. (c) Would the actual temperature of frothy milk be higher than, equal to or lower than the value found in (b)? Explain. 4
Exposition : attacking strategy Task 2 Step 1 in attacking a question calling for an Exposition answer: Indentifying the subject matter to make judgment on. 5
Exposition : tackling strategy E.g. applying backward reasoning 2012 DSE 1B Q1c Steps Referring to the Question actual temp of frothy milk (judge: higher, equal, than in (b)) 1. subject matter to make judgment on 2. relevant Physics knowledge Ht lost (hotter objs) = ht absorbed (colder objs) 3. apply the knowledge to the question to deduce a conclusion for the judgment to be made In (b): Ht lost by steam = ht absorbed by milk ; But there are other objs absorbing ht from steam (e.g. the jug, surrounding air) , not all ht from steam to milk; (b) over-estimated. Temp should (actually) be lower. Note: a. knowledge already used in earlier part of question; b. the explanation is already in #3; c. short-hand and symbol used for efficiency. 6
Answer as Exposition Writing The actual temperature of the milk would be lower than the value found in (b). Statement of Position / judgment It is because some energy will be lost to the surroundings, e.g., the air and the jug. Argument / Explanation Thus, the actual temperature will be lower than that found in (b). Reinforcement of Position (may be omitted for short essay) 7
Exposition : tackling strategy Understanding of Exposition Genre Could NOT replace Understanding of Physics, which is essential in the reasoning 8
Backward Reasoning Ex Task 3a Task 3b Task 3c Task 3d 9
