Photoelectric Effect and Electron Volts

NCEA Level 3 Physics Year 13 Understanding quantum phenomena

WALT - We Are Learning To

Explain the photoelectric effect phenomenon Describe how photoelectric cells function Define and calculate using electron volts (eV) Apply quantum theory to real-world applications

Success Criteria

I can explain why classical physics failed to explain photoelectric effect I can describe Einstein's photon model I can calculate energy using E = hf I can convert between joules and electron volts I can explain applications in modern technology

What happens when light hits metal?

Think about: Why do some metals spark when hit by light? What determines if electrons are emitted? Classical vs quantum predictions

Historical Background

Heinrich Hertz (1887) - First observed photoelectric effect Classical physics predicted different results Puzzle: Why did frequency matter more than intensity? Einstein's 1905 explanation won Nobel Prize (1921)

The Classical Physics Problem

Einstein's Revolutionary Idea

"Light consists of discrete packets of energy called photons. Each photon carries energy E = hf, where h is Planck's constant and f is frequency."

The Photoelectric Effect Explained

Photons hit electrons in metal surface Each photon transfers ALL its energy to ONE electron If photon energy ≥ work function, electron escapes Excess energy becomes kinetic energy of electron

Key Equation: Einstein's Photoelectric Equation

E_photon = Work Function + Kinetic Energy hf = φ + ½mv² Where: h = Planck's constant (6.63 × 10⁻³⁴ J·s) f = frequency of light φ = work function of metal

Differentiated Learning Activity

Foundation Level: Identify which factors affect photoelectric effect Standard Level: Calculate photon energy using E = hf Advanced Level: Solve complex photoelectric problems with multiple variables Extension: Research applications in solar panels

What is an Electron Volt (eV)?

Unit of energy commonly used in atomic physics Energy gained by one electron moving through 1 volt 1 eV = 1.6 × 10⁻¹⁹ joules Much more convenient than joules for atomic-scale energies

Energy Unit Conversions

{"left":"Joules (J)\nSI base unit\nVery large for atomic scales\nUsed in macroscopic physics","right":"Electron Volts (eV)\nConvenient for atomic physics\n1 eV = 1.6 × 10⁻¹⁹ J\nTypical atomic energies: 1-10 eV"}