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Chapter 7: Problem 10

Give two examples of processes that are modeled by exponential decay.

Short Answer

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#Question# Provide two examples of processes that are modeled by exponential decay and briefly explain how they are modeled using exponential decay equations. #Answer# 1) Radioactive Decay: In this process, the number of radioactive atoms decreases over time following an exponential decay model given by N(t) = N * e^{-位t}, where N(t) is the number of atoms remaining at time t, N is the initial number of atoms, 位 is the decay constant, and e is the base of the natural logarithm. 2) Cooling of an Object: Newton's law of cooling states that the rate of an object's cooling is proportional to the difference between the object's temperature and the surrounding environment's temperature. The temperature of the object at time t can be modeled by T(t) = T_e + (T0 - T_e) * e^{-kt}, where T(t) is the temperature of the object at time t, T0 is the initial temperature, T_e is the surrounding environment's temperature, e is the base of the natural logarithm, and k is a constant related to the object's cooling properties.

Step by step solution

01

Example 1: Radioactive Decay

Radioactive decay is a process through which an unstable atomic nucleus loses energy by emitting radiation. In this process, the number of atoms of a radioactive material decreases over time, following an exponential decay model. Suppose we have an initial amount of N radioactive atoms and the decay constant is denoted by 位. The number of remaining atoms after a certain time t will be given by: N(t) = N * e^{-位t} In this equation, N(t) represents the number of atoms remaining at time t, N is the initial number of atoms, 位 is the decay constant and e is the base of the natural logarithm.
02

Example 2: Cooling of an Object

Another example of a process modeled by exponential decay is the cooling of an object over time. Newton's law of cooling states that the rate at which an object cools is proportional to the difference between the object's temperature and the temperature of the surrounding environment. Suppose we have an object with an initial temperature T(0) = T0 and the surrounding environment temperature being T_e. The temperature of the object at time t will be given by: T(t) = T_e + (T0 - T_e) * e^{-kt} Where T(t) represents the temperature of the object at time t, T0 is the initial temperature of the object, T_e is the temperature of the surrounding environment, e is the base of the natural logarithm and k is a constant related to the object's cooling properties.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Radioactive Decay
At its core, radioactive decay is a fundamental process by which an unstable atomic nucleus releases energy to reach a more stable state. Different isotopes (or versions of an element with varying numbers of neutrons) decay at different rates, and this rate of decay is predictable, described by an elegant mathematical model.

Most importantly, the decay doesn't happen all at once but gradually over time, and the rate of decay is proportional to the amount of substance remaining. This is what scientists refer to as an exponential decay process. The formula you see in exercises, N(t) = N \( e^{-\lambda t} \), succinctly captures this relationship. N(t) is the remaining quantity of the substance at time t, N is the initial quantity, and \(\lambda\) is a positive constant specific to the substance, aptly named the decay constant, indicative of the speed at which the substance undergoes decay.

Key takeaway? As time passes, the quantity of the radioactive substance decreases exponentially, never reaching zero but getting infinitesimally close over an infinite amount of time.
Newton's Law of Cooling
Closely related to the pattern of exponential decay, Newton's law of cooling reveals how the temperature of a warm object decreases over time. Similar to radioactive substances, the cooling of an object is not at a constant rate but depends on the difference between the object's current temperature and the ambient temperature of its surroundings.

Mathematically, Newton described this phenomenon with the equation T(t) = T_e + (T0 - T_e) \( e^{-kt} \). Here, T(t) symbolizes the temperature of the object at any time t, T_e signifies the environment鈥檚 constant temperature, and T0 is what the object's initial temperature was. The k is another decay constant, altering how fast the object cools depending on its properties, such as thermal conductivity and size.

Essentially, the exponential factor \( e^{-kt} \) governs the rate of temperature change, showcasing that as the difference in temperatures drops, the cooling slows down, leading to a gradual stabilization of the object鈥檚 temperature with the environment over time.
Decay Constant
The idea of a decay constant is pivotal in understanding exponential decay. It's not just a number; it symbolizes how swiftly a quantity decreases over time. Specific to each process, be it radioactive decay or cooling, the constant tells us the proportion of the substance or the difference in temperature that decays in a unit of time.

Relationship with Half-Life

Take radioactive decay, for instance. The decay constant \(\lambda\) is intertwined with another concept called the half-life, the time it takes for half the radioactive atoms in a sample to decay. The two are related mathematically by the natural logarithm: half-life = \( \frac{\ln(2)}{\lambda} \), where \( \ln \) is the natural logarithm.

The higher the decay constant, the faster the quantity diminishes, indicating a reactive substance or a highly conductive material in the context of cooling. Thus, by understanding the decay constant, one can predict the longevity of a substance or the cooling time for a meal straight out of the oven.
Natural Logarithm Base e
Finally, to fully grasp concepts like decay constant and exponential decay processes, a solid understanding of the natural logarithm base e is essential. What's special about e, approximately equal to 2.71828, is it arises naturally in various contexts of mathematics, especially in continuous growth or decay situations.

The natural logarithm, denoted by ln, is the inverse operation of taking e to a power. Specifically, for a positive number x, ln(x) answers the question: 'To what power must we raise e to get x?'. This function is key in calculating the half-life from the decay constant as mentioned earlier and appears in the formulas that describe both radioactive decay and Newton's law of cooling.

In sum, this quirky number e is not just any ordinary constant but the cornerstone of accurately modeling processes that change exponentially over time, helping us untangle the mysteries of atomic nuclei or predict when a warm pie will be cool enough to eat without burning our tongues.

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