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

Giancoli Douglas 5th edition

Ch. 20 - Second Law of Thermodynamics

Problem 60a

Chapter 20, Problem 60a

Suppose that you repeatedly shake six coins in your hand and drop them on the floor. Construct a table showing the number of microstates that correspond to each macrostate. What is the probability of obtaining three heads and three tails?

Verified step by step guidance

Understand the problem: A macrostate is defined by the number of heads and tails (e.g., 3 heads and 3 tails), while a microstate is a specific arrangement of the coins (e.g., HHTTHT). The goal is to calculate the number of microstates for each macrostate and determine the probability of obtaining 3 heads and 3 tails.

Step 1: Use the binomial coefficient formula to calculate the number of microstates for each macrostate. The formula is:

C (n, r) = \frac{n!}{r! (n - r)!}

, where

n

is the total number of coins (6 in this case) and

r

is the number of heads.

Step 2: Construct a table for all possible macrostates (0 heads, 1 head, ..., 6 heads). For each macrostate, calculate the number of microstates using the binomial coefficient formula. For example, for 3 heads and 3 tails, calculate:

C (6, 3) = \frac{6!}{3! (6 - 3)!}

Step 3: Calculate the total number of microstates by summing up the microstates for all macrostates. The total number of microstates is given by

2^{6}

, since each coin has two possible outcomes (head or tail).

Step 4: Determine the probability of obtaining 3 heads and 3 tails. The probability is given by the ratio of the number of microstates for the desired macrostate (3 heads and 3 tails) to the total number of microstates. Use the formula:

P = \frac{C (6, 3)}{2^{6}}

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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, when flipping coins, each unique arrangement of heads and tails represents a microstate, whereas the overall count of heads and tails (e.g., three heads and three tails) represents a macrostate.

Combinatorics

Combinatorics is a branch of mathematics dealing with counting, arrangement, and combination of objects. In the context of the coin problem, it helps determine the number of ways to achieve a specific outcome, such as three heads and three tails, by using the binomial coefficient, which calculates the number of ways to choose a subset from a larger set.

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 scenario, the probability of obtaining three heads and three tails can be calculated by dividing the number of favorable microstates (ways to achieve three heads and three tails) by the total number of microstates for six coin flips.

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Probability Distribution Graph

Related Practice

Textbook Question

Suppose that you repeatedly shake six coins in your hand and drop them on the floor. Construct a table showing the number of microstates that correspond to each macrostate. What is the probability of obtaining six heads?

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Textbook Question

Use Eq. 20–14 to determine the entropy of each of the five macrostates listed in Table 20–1 on page 595.

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Textbook Question

Why would you expect the total entropy change in a Carnot cycle to be zero? Do a calculation to show that it is zero.

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Textbook Question

(II) Calculate the probabilities, when you throw two dice, of obtaining a 7.

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Textbook Question

(II) Calculate the probabilities, when you throw two dice, of obtaining an 11.

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Textbook Question

A general theorem states that the amount of energy that becomes unavailable to do useful work in any process is equal to T_L∆S, where T_L is the lowest temperature available and ∆S is the total change in entropy during the process. Show that this is valid in the specific cases of a falling rock that comes to rest when it hits the ground.