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A \(10.0-\mathrm{g}\) marble is gently placed on a horizontal tabletop that is 1.75 \(\mathrm{m}\) wide. (a) What is the maximum uncertainty in the horizontal position of the marble? (b) According to the Heisenberg uncertainty principle, what is the minimum uncertainty in the horizontal velocity of the marble? (c) In light of your answer to part (b), what is the longest time the marble could remain on the table? Compare this time to the age of the universe, which is approximately 14 billion years. (Hint: Can you know that the horizontal velocity of the marble is exactly zero?)

Short Answer

Expert verified
(a) 1.75 m; (b) Use the Heisenberg principle to find \( \Delta v \); (c) Calculate and compare with 14 billion years.

Step by step solution

01

Identifying Maximum Uncertainty in Position

The maximum uncertainty in the horizontal position of the marble can be considered as the width of the table itself since the marble could be anywhere across the table. Therefore, the maximum uncertainty, \( \Delta x \), is 1.75 m.
02

Heisenberg Uncertainty Principle Formula

The Heisenberg Uncertainty Principle can be expressed as \( \Delta x \cdot \Delta p \geq \frac{\hbar}{2} \), where \( \Delta x \) is the uncertainty in position, \( \Delta p \) is the uncertainty in momentum, and \( \hbar \) is the reduced Planck's constant, approximately \( 1.0545718 \times 10^{-34} \) Js.
03

Calculating Minimum Uncertainty in Momentum

To find the minimum uncertainty in momentum \( \Delta p \), rearrange the Heisenberg uncertainty formula: \( \Delta p = \frac{\hbar}{2 \cdot \Delta x} \). Substitute \( \Delta x = 1.75 \) m into the equation: \( \Delta p = \frac{1.0545718 \times 10^{-34}}{2 \times 1.75} \) kg m/s.
04

Calculating Minimum Uncertainty in Velocity

The uncertainty in momentum \( \Delta p \) is related to the uncertainty in velocity \( \Delta v \) by the equation \( \Delta p = m \cdot \Delta v \), where \( m = 0.01 \) kg is the mass of the marble. Solve for \( \Delta v \): \( \Delta v = \frac{\Delta p}{m} \). Substitute the computed \( \Delta p \) from Step 3.
05

Determining Longest Time on Table

The time \( t \) the marble could remain on the table without leaving can be estimated by \( t = \frac{\Delta x}{\Delta v} \). Substitute \( \Delta x = 1.75 \) m and the computed \( \Delta v \) from Step 4. Evaluate \( t \) to compare with the age of the universe.

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Key Concepts

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

Maximum Uncertainty in Position
In the context of the Heisenberg Uncertainty Principle, the maximum uncertainty in position refers to how precisely we can determine where an object is located. For our marble resting on the tabletop, this uncertainty is determined by the table's width. Since the marble can be anywhere from one edge to the other, this makes the maximum uncertainty, \( \Delta x \), equal to the entire width of the table, which is 1.75 meters. This concept highlights that even though the marble appears to be stationary, quantum mechanics suggests there's a range over which its exact position remains uncertain. - **Key Points:** - Uncertainty covers the range within which the marble could be positioned. - The entire width of the table represents the maximum possible uncertainty in the marble's position.This example demonstrates the practical application of quantum principles to everyday objects, showing that uncertainty is not just an element of microscopic particles but affects larger systems when considered through the lens of quantum mechanics.
Minimum Uncertainty in Velocity
When discussing minimum uncertainty in velocity, we're looking at how accurately we can measure the speed at which the marble moves horizontally. Given the Heisenberg Uncertainty Principle, once the uncertainty in position is large (as it is here with the table's width), the uncertainty in momentum and, thus, velocity, must meet certain conditions. This relationship is expressed in the principle's equation: \( \Delta x \cdot \Delta p \geq \frac{\hbar}{2} \). - **Calculating Velocity Uncertainty:** - First, find the uncertainty in momentum using \( \Delta p = \frac{\hbar}{2 \cdot \Delta x} \). - Convert the uncertainty in momentum to velocity by dividing \( \Delta p \) by the marble's mass.This calculation illustrates that even a stationary object is described by quantum mechanics to have a minimum uncertainty in its velocity, as precise measurements of position lead to greater uncertainty in speed. This fundamental trade-off ensures that either position or velocity measurements remain imprecise without influencing each other.
Momentum Uncertainty
Momentum uncertainty is the indefinite range in the product of mass and velocity, which is tied heavily to the Uncertainty Principle. In our marble example, momentum uncertainty stretches from the precision of its position and velocity measurements. - **Key Formula:** - The formula used is \( \Delta p = \frac{\hbar}{2 \cdot \Delta x} \), which gives the minimum uncertainty in the marble's momentum. - Here, \( \Delta x \) is the uncertainty in position (1.75 m), and \( \Delta p \) is the resulting momentum uncertainty.To fully understand momentum uncertainty, it's crucial to remember that momentum is a variable product of an object's mass and velocity. As such, a reduced certainty in one aspect increases the necessary uncertainty in the other, a unique aspect of quantum mechanics that dictates that we can never know both properties with absolute precision. This means there is always a fundamental limit placed on our knowledge within the quantum world.

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Most popular questions from this chapter

Blue Supergiants. A typical blue supergiant star (the type that explodes and leaves behind a black hole) has a surface temperature of \(30,000 \mathrm{K}\) and a visual luminosity \(100,000\) times that of our sun. Our sun radiates at the rate of \(3.86 \times 10^{26} \mathrm{W}\) .(Visual luminosity is the total power radiated at visible wavelengths.) (a) Assuming that this star behaves like an ideal blackbody, what is the principal wavelength it radiates? Is this light visible? Use your answer to explain why these stars are blue. (b) If we assume that the power radiated by the star is also \(100,000\) times that of our sun, what is the radius of this star? Compare its size to that of our sun, which has a radius of \(6.96 \times 10^{5} \mathrm{km}\) . (c) Is it really correct to say that the visual luminosity is proportional to the total power radiated? Explain.

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