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Ch. 20 - Second Law of Thermodynamics
Giancoli Douglas - Physics for Scientists and Engineers 5th edition
Giancoli Douglas5th editionPhysics for Scientists and EngineersISBN: 9780137488179Not the one you use?Change textbook
Chapter 20, Problem 89b

A bowl contains many red, orange, and green jelly beans, in equal numbers. You are to make a line of 3 jelly beans by randomly taking 3 beans from the bowl. Construct a table showing the number of microstates that correspond to each macrostate. Then, determine the probability of all 3 beans red.

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Step 1: Understand the problem. A macrostate refers to the overall outcome (e.g., all 3 beans red, 2 red and 1 green, etc.), while a microstate refers to a specific arrangement of jelly beans that results in a given macrostate. Since the bowl contains equal numbers of red, orange, and green jelly beans, the probability of picking any color is equal.
Step 2: Construct a table of macrostates and microstates. For 3 jelly beans, the possible macrostates are: (a) all 3 beans red, (b) 2 red and 1 of another color, (c) 1 red and 2 of another color, and (d) all 3 beans of different colors. For each macrostate, calculate the number of microstates using combinations and permutations.
Step 3: Calculate the number of microstates for the macrostate 'all 3 beans red.' Since all beans are red, there is only 1 microstate: {R, R, R}.
Step 4: Calculate the total number of possible microstates. Since there are 3 colors and 3 jelly beans are chosen, the total number of microstates is given by \(3^3 = 27\), as each jelly bean can independently be red, orange, or green.
Step 5: Determine the probability of the macrostate 'all 3 beans red.' The probability is the ratio of the number of microstates for this macrostate to the total number of microstates. Using the formula \(P = \frac{\text{Number of microstates for the macrostate}}{\text{Total number of microstates}}\), substitute the values to find the probability.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Microstates and Macrostates

In statistical mechanics, a microstate refers to a specific detailed configuration of a system, while a macrostate is defined by macroscopic properties like temperature or pressure. For example, in the jelly bean scenario, each unique arrangement of jelly beans represents a microstate, while the overall color distribution (e.g., all red) represents a macrostate. Understanding this distinction is crucial for calculating probabilities.
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Microstates and Macrostates of a System

Combinatorics

Combinatorics is a branch of mathematics dealing with counting, arrangement, and combination of objects. In this context, it helps determine the number of ways to select jelly beans from the bowl. For example, the number of ways to choose 3 jelly beans from equal numbers of red, orange, and green can be calculated using combinations, which is essential for finding the total number of microstates.

Probability

Probability quantifies the likelihood of an event occurring, expressed as a ratio of favorable outcomes to the total number of possible outcomes. In this case, to find the probability of drawing 3 red jelly beans, one must divide the number of favorable microstates (all red) by the total number of microstates for drawing 3 beans. This concept is fundamental for answering the question regarding the likelihood of specific outcomes.
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Related Practice
Textbook Question

A dehumidifier removes water vapor from air and has been referred to as a “refrigerator with an open door.” The humid air is pulled in by a fan and passes over a cold coil, whose temperature is less than the dew point, and some of the air’s water condenses. After this water is extracted, the air is warmed back to its original temperature and sent into the room. In a well-designed dehumidifier, the heat that is removed by the cooling coil mostly comes from the condensation of water vapor to liquid, and this heat is used to re-warm the air. Estimate how much water is removed in 1.0 h by an ideal dehumidifier, if the temperature of the room is 25°C, the water condenses at 8°C, and the dehumidifier does work at the rate of 550 W of electrical power.

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Textbook Question

A bowl contains many red, orange, and green jelly beans, in equal numbers. You are to make a line of 3 jelly beans by randomly taking 3 beans from the bowl. Construct a table showing the number of microstates that correspond to each macrostate.

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Textbook Question

Trees can help a bit to offset the buildup of CO₂ due to burning coal and other fossil fuels. CO₂ can be absorbed by tree foliage. Trees use the carbon to grow, and release O₂ into the atmosphere. Suppose a refrigerator uses 600 kWh of electricity per year (about 2 x 10⁹ J) from a 33% efficient coal-fired power plant. Burning 1 kg of coal releases about 2 x 10⁷ J of energy. Assume coal is all carbon, which when burned in air becomes CO₂.

(a) How much coal is burned per year to run this refrigerator?

(b) Assuming a forest can capture 1700 kg of carbon per hectare ( = 10, 000 m²) per year, estimate how many square meters of forest are needed to capture the carbon (in the form now of CO₂) emitted by the refrigerator in (a).

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Textbook Question

Suppose a heat pump has a stationary bicycle attachment that allows you to provide the work instead of using an electrical wall outlet. If your heat pump has a coefficient of performance of 2.0 and you can cycle at a racing pace output of about 200 W for a half hour, how much heat can you provide?

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Textbook Question

Rank the following five-card hands in order of increasing probability: (a) four aces and a king; (b) six of hearts, eight of diamonds, queen of clubs, three of hearts, jack of spades; (c) two jacks, two queens, and an ace; and (d) any hand having no two equal-value cards (no pairs, etc.). Discuss your ranking in terms of microstates and macrostates.

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