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Ch 41: Atomic Physics
Knight Calc - Physics for Scientists and Engineers 5th Edition
Knight Calc5th EditionPhysics for Scientists and EngineersISBN: 9780137344796Not the one you use?Change textbook
Chapter 41, Problem 27a

There exist subatomic particles whose spin is characterized by s = 1, rather than the s = ½ of electrons. These particles are said to have a spin of one. What is the magnitude ( as a multiple of ℏ ) of the spin angular momentum S for a particle with a spin of one?

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1
Understand the concept of spin angular momentum: The spin angular momentum of a particle is given by the formula \( S = \sqrt{s(s+1)} \hbar \), where \( s \) is the spin quantum number and \( \hbar \) is the reduced Planck's constant.
Identify the given spin quantum number: In this problem, the spin quantum number \( s \) is provided as \( s = 1 \).
Substitute the value of \( s \) into the formula: Replace \( s \) with 1 in the formula \( S = \sqrt{s(s+1)} \hbar \), resulting in \( S = \sqrt{1(1+1)} \hbar \).
Simplify the expression inside the square root: Calculate \( 1+1 \), which equals 2, so the formula becomes \( S = \sqrt{1 \cdot 2} \hbar \).
Simplify further to find the magnitude: The expression simplifies to \( S = \sqrt{2} \hbar \), which represents the magnitude of the spin angular momentum as a multiple of \( \hbar \).

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Spin Angular Momentum

Spin angular momentum is a fundamental property of particles, akin to classical angular momentum, but it arises from quantum mechanical effects. It is quantized, meaning it can only take on certain discrete values. For a particle with spin quantum number s, the magnitude of its spin angular momentum is given by the formula S = √(s(s + 1))ℏ, where ℏ is the reduced Planck's constant.
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Quantum Number

Quantum numbers are values that describe the quantized properties of particles in quantum mechanics. The spin quantum number, denoted as s, indicates the intrinsic angular momentum of a particle. For particles with spin s = 1, they can have three possible projections of spin along a chosen axis: +1, 0, and -1, which correspond to the allowed states of the particle.
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Reduced Planck's Constant (ℏ)

The reduced Planck's constant, denoted as ℏ (h-bar), is a fundamental constant in quantum mechanics, defined as ℏ = h/(2π), where h is the Planck constant. It plays a crucial role in quantifying angular momentum and other quantum properties. In the context of spin, it serves as a scaling factor that relates the quantum mechanical description of spin to classical angular momentum.
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