Quantum Mechanics: Particle Motion and Zero-Point Energy

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Questions and Answers

What happens to the uncertainty on P when the width of the well decreases?

It becomes zero

It remains the same

It increases (correct)

It decreases

Why does the zero-point energy not vanish even when the width of the well increases?

It only occurs in macroscopic systems

It reflects the minimum motion of a particle due to localization (correct)

It is a classical mechanics concept

It is a result of the uncertainty principle

What is the difference between the lowest energy state in classical mechanics and quantum mechanics?

Quantum mechanics minimizes the potential energy alone

Quantum mechanics has a higher energy state (correct)

Classical mechanics has zero kinetic energy

Classical mechanics has a higher energy state

What would happen to atoms if there were no zero-point motion?

The electrons would fall into the nuclei Signup and view all the answers

What is the role of zero-point energy in the stability of helium at very low temperatures?

It prevents helium from freezing Signup and view all the answers

In which systems is the zero-point energy infinitesimally small?

Macroscopic systems Signup and view all the answers

What is the relationship between the uncertainty in momentum and the width of the well?

They are inversely proportional Signup and view all the answers

Why does the particle move faster and faster as the width of the well decreases?

Due to an increase in the uncertainty on P Signup and view all the answers

What is the zero-point energy of a 100 g ball confined to a 5 m long line?

1.25 × 10^(-49) eV Signup and view all the answers

Why is the zero-point energy important in microscopic systems?

Because it is comparable to the binding energy of a hydrogen electron Signup and view all the answers

What is the mass of an oxygen atom confined to a 2 × 10^(-10) m lattice?

26 × 10^(-27) kg Signup and view all the answers

What is the zero-point energy of an electron confined to an atom?

5 × 10^(-18) J Signup and view all the answers

What happens to the zero-point energy as the system changes from macroscopic to microscopic?

It increases Signup and view all the answers

What is the zero-point energy of an oxygen atom confined to a 2 × 10^(-10) m lattice?

5 × 10^(-4) eV Signup and view all the answers

Why is the zero-point energy negligible for macroscopic objects?

Because it is too small to be detected Signup and view all the answers

What is the approximate binding energy of a hydrogen electron?

14 eV Signup and view all the answers

What is the characteristic of the energy levels in the infinite square well potential?

They are non-degenerate with only one eigenfunction for each energy level Signup and view all the answers

Why do the wave functions corresponding to different energy levels need to be orthogonal?

To preserve the normalization of the wave functions Signup and view all the answers

What is the general form of the solution to the time-dependent Schrödinger equation for stationary states?

U(x,t) = On(x) e^(iEnt/h) Signup and view all the answers

What is the reason why there is no state with zero energy for a square well potential?

Because of the uncertainty principle Signup and view all the answers

What is the minimum momentum uncertainty that arises from the localization of the particle's motion?

h/a Signup and view all the answers

What is the order of the minimum kinetic energy that arises from the localization of the particle's motion?

h^2/ma^2 Signup and view all the answers

What is the exact value of the zero-point energy in the infinite square well potential?

h^2/2ma^2 Signup and view all the answers

What is the physical principle that leads to the existence of a minimum kinetic energy in the infinite square well potential?

Heisenberg's uncertainty principle Signup and view all the answers

Study Notes

Zero-Point Energy

The zero-point energy of a particle in a bound state potential is a fundamental concept in quantum mechanics, where the lowest energy state has an energy higher than the minimum of the potential energy.
This is in contrast to classical mechanics, where the lowest possible energy is equal to the minimum value of the potential energy, with zero kinetic energy.
The zero-point energy reflects the necessity of a minimum motion of a particle due to localization.
It occurs in all bound state potentials and has far-reaching physical consequences in the microscopic world.

Characteristics of Zero-Point Energy

The zero-point energy is inversely proportional to the width of the well.
As the width of the well decreases, the zero-point energy increases, making the particle move faster and faster.
Conversely, if the width of the well increases, the zero-point energy decreases, but it never vanishes.
The zero-point energy is negligible for macroscopic objects but important for microscopic systems.

Examples of Zero-Point Energy

For a 100 g ball confined to a 5 m long line, the zero-point energy is approximately 1.25 × 10^(-49) eV, which is too small to be detected.
For an oxygen atom confined to a 2 × 10^(-10) m lattice, the zero-point energy is approximately 3 × 10^(-4) eV.
For an electron confined to an atom, the zero-point energy is approximately 30 eV, which is important at the atomic scale.

Symmetric Potential Well

If the potential is translated to the left by a distance of a/2 to become symmetric, none of the energy levels are degenerate, and the wave functions corresponding to different energy levels are orthogonal.
The most general solutions of the time-dependent Schrödinger equation are given by a linear combination of the eigenfunctions.

Importance of Zero-Point Energy

The zero-point energy prevents atoms from being unstable, as electrons would fall into the nuclei without it.
It also prevents helium from freezing at very low temperatures.

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Description

This quiz explores the relationship between particle motion and zero-point energy in quantum mechanics, discussing how the uncertainty principle affects particle behavior in a potential well.