QNT-14

Photoelectric equation

Kmax = hf − φ. Light above the work function frees electrons.

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QuantaEinstein 1905

Governing equation

K_{\max}=hf-\varphi

where

f: Frequency (PHz)
\varphi: Work function (eV)
K_{max}: Max kinetic energy (eV)

Lecture brief

Historical brief

Planck (1900), Einstein’s photoelectric law, Bohr, de Broglie, Heisenberg and Schrödinger’s 1926 equation rebuilt matter as amplitude. These sheets are the first solvable models: wells, spin, tunneling, uncertainty. This sheet (QNT-14 — Photoelectric equation) is the form associated with Einstein 1905. Working symbols: $f$ , $\varphi$ $\rightarrow$ $K_{max}$ . Stopping potential e Vs = Kmax. Intensity sets the current, not Kmax.

Purpose

Purpose: compute

K_{max}

from

f

\varphi

in Quantum mechanics via

K_{\max}=hf-\varphi

Kmax = hf − φ. Light above the work function frees electrons. Use it when a real quantum mechanics question must be answered in SI before a code check.

Live realistic example

In symbols

Live case. Given

f = 0.800\,\mathrm{PHz}

\varphi = 2.300\,\mathrm{eV}

, the governing relation

K_{\max}=hf-\varphi

yields

K_{max} = 1.009\,\mathrm{eV}

. A metal, a photon, an escaping electron. Move a slider: the numbers are this situation, not a canned story.

Calculator

Inputs

Frequency f0.8 PHzWork function \varphi2.3 eV

Outputs

Max kinetic energy K_{max}1.009 eV

Reading speed

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Narration of this film

A metal, a photon, an escaping electron.

Stopping potential e Vs = Kmax. Intensity sets the current, not Kmax.

Reading speed

Watch on YouTube