---
title: "Planck's Constant — AP Physics 2 Definition & Exam Guide"
description: "Planck's constant (h = 6.63 × 10⁻³⁴ J·s) links a photon's energy to its frequency via E = hf. It powers the photoelectric effect and de Broglie wavelength in Unit 7."
canonical: "https://fiveable.me/ap-physics-2-revised/key-terms/plancks-constant"
type: "key-term"
subject: "AP Physics 2"
---

# Planck's Constant — AP Physics 2 Definition & Exam Guide

## Definition

Planck's constant (symbolized as h) is a fundamental constant in quantum mechanics that relates the energy of a photon to its frequency. It is used to calculate the energy levels and behavior of particles at the atomic and subatomic scale.

## Related Study Guides

- [7.7 Wave Functions and Probability](/ap-physics-2-revised/unit-7/wave-functions-probability/study-guide/HYPoYs3xG1I9JCLLP09U)
- [7.5 Properties of Waves and Particles](/ap-physics-2-revised/unit-7/properties-waves-particles/study-guide/gXV2Vd4gN69ociflUUAD)
- [7.6 Photoelectric Effect](/ap-physics-2-revised/unit-7/photoelectric-effect/study-guide/r1hPbt2hCbd4ymj2o7Um)

## Review

### Related Terms

- [Photon](/ap-physics-2-revised/key-terms/photon): A fundamental particle of light that carries energy in discrete packets.
- Energy Level: The specific allowed energies an electron can have in an atom or molecule.
- [Quantum Mechanics](/ap-physics-2-revised/key-terms/quantum-mechanics): The branch of physics that describes the behavior of matter and energy at extremely small scales, incorporating principles such as wave-particle duality and quantization.