Modern Physics

Moseley's Law

f=a(Zb)\sqrt{f} = a(Z - b)

Relates characteristic X-ray frequencies to atomic number. The screening constant b accounts for shielding by inner electrons (b ≈ 1 for Kα lines, b ≈ 7.4 for Lα lines).

Variables

f
Characteristic X-ray frequency
Hz
a
Proportionality constant
Hz^(1/2)
Z
Atomic number
unitless
b
Screening constant
unitless

Derivation

Moseley discovered this empirically, which helped establish atomic number as fundamental to element identity.

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Common questions

What is the Moseley's Law formula?

Moseley's Law is written √(f) = a(Z - b). Relates characteristic X-ray frequencies to atomic number. The screening constant b accounts for shielding by inner electrons (b ≈ 1 for Kα lines, b ≈ 7.4 for Lα lines). It belongs to Modern Physics, under Atomic Physics.

What are the units in √(f) = a(Z - b)?

In SI units, f is characteristic x-ray frequency, measured in Hz; a is proportionality constant, measured in Hz^(1/2); Z is atomic number (dimensionless); b is screening constant (dimensionless).

How is the Moseley's Law formula derived?

Moseley discovered this empirically, which helped establish atomic number as fundamental to element identity. The result is √(f) = a(Z - b).