Ch 39: Wave Functions and Uncertainty

Knight Calc - Physics for Scientists and Engineers 5th Edition

Knight Calc5th EditionPhysics for Scientists and EngineersISBN: 9780137344796당신이 사용하는 게 아니라요?교과서 변경

Knight Calc 5th Edition

Ch 39: Wave Functions and Uncertainty

문제 43a

39장, 문제 43a

Heavy nuclei often undergo alpha decay in which they emit an alpha particle (i.e., a helium nucleus). Alpha particles are so tightly bound together that it’s reasonable to think of an alpha particle as a single unit within the nucleus from which it is emitted. A ²³⁸U nucleus, which decays by alpha emission, is 15 fm in diameter. Model an alpha particle within a ²³⁸U nucleus as being in a one-dimensional box. What is the maximum speed an alpha particle is likely to have?

검증된 단계별 안내

Model the alpha particle as a particle in a one-dimensional box. The energy levels of a particle in a one-dimensional box are given by the formula:

E_{n} = \frac{n^{2}}{h} / 8 m L^{2}

, where n is the quantum number, h is Planck's constant, m is the mass of the particle, and L is the length of the box.

The diameter of the uranium nucleus is given as 15 fm (femtometers), so the length of the one-dimensional box is approximately

L = 15 fm = 15 × 10

^-15 m.

The mass of the alpha particle is approximately

m = 6.64 × 10

^-27 kg. Use this value for the mass in the energy formula.

The maximum speed corresponds to the maximum energy, which occurs at the first energy level (

n = 1

). Calculate the energy using the formula for

E_{1}

and substitute the values for

h

m

, and

L

Once the energy is calculated, use the relationship between kinetic energy and speed:

E = \frac{1}{2} m v^{2}

. Solve for

v

(speed) by rearranging the equation:

v = \sqrt{\frac{2}{E}}

. Substitute the calculated energy and the mass of the alpha particle to find the maximum speed.

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주요 개념

질문에 올바르게 답하기 위해 반드시 이해해야 하는 핵심 개념들은 다음과 같습니다.

Quantum Mechanics and Particle in a Box Model

In quantum mechanics, the particle in a box model describes a quantum particle confined to a one-dimensional space with infinitely high potential walls. This model helps to determine the energy levels and wave functions of the particle. For an alpha particle in a nucleus, this model allows us to calculate its maximum speed based on its quantized energy states.

Heisenberg Uncertainty Principle

The Heisenberg Uncertainty Principle states that it is impossible to simultaneously know both the position and momentum of a particle with absolute precision. This principle is crucial in quantum mechanics, as it implies that the more precisely we know the position of the alpha particle within the nucleus, the less precisely we can know its momentum, affecting its calculated speed.

Kinetic Energy and Speed Relationship

The kinetic energy of a particle is directly related to its speed, given by the equation KE = 1/2 mv², where m is the mass and v is the speed. In the context of the alpha particle, understanding this relationship allows us to derive its maximum speed from the energy levels determined by the particle in a box model, providing insight into its behavior during alpha decay.

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