Indiana Science HS-PSII-9.4

ScienceGrades 9–12Physical Science

The Standard

Describe the slope of the graphical representation of the kinetic energy of a photoelectron vs. frequency in terms of Planck’s constant.

Indiana Academic Standards for Science (2023) · Particle and Wave Nature of Light

Teacher's field guide

What Students Need to Do: Students read a graph of electron kinetic energy against light frequency. They find the slope using two points above the cutoff frequency and connect it to Planck’s constant.
What Mastery Looks Like: Students calculate the slope as about 6.63 × 10⁻³⁴ J·s. They explain that different metals can have different cutoff frequencies but the same slope.
Common Misconceptions: Students may mistake the slope for the metal’s work function or think it changes with the metal. Some use light intensity instead of frequency, or plot energy values below the cutoff, where no electrons are emitted.
How to Assess It: Exit ticket: Electron energies are 1.00 × 10⁻¹⁹ J at 8 × 10¹⁴ Hz and 2.32 × 10⁻¹⁹ J at 10 × 10¹⁴ Hz. Find the slope and name the constant it represents.

Lesson moves

Plot frequency-energy pairs (8, 1.00), (9, 1.66), and (10, 2.32) on graph paper, using 10¹⁴ Hz and 10⁻¹⁹ J; find the slope.
Show two parallel energy-frequency lines for different metals; ask students why their cutoff frequencies differ but their slopes match.
Give pairs cards with changes in frequency and kinetic energy; have them match cards whose ratio is 6.63 × 10⁻³⁴ J·s.
Use the class graph as a photocell calibration chart; ask students to predict electron energy at 9.5 × 10¹⁴ Hz.

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A ready-to-print activity worksheet aligned to HS-PSII-9.4, with an answer key for the teacher on its own page. No account needed.

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