Lesson Plan

• Describe the Stefan–Boltzmann law and its variables.
• Apply the rearranged formula to calculate stellar radii from given luminosities and temperatures.
• Convert astronomical units to SI units and interpret the physical meaning of the results.
• Identify common errors (unit mismatches, missing T⁴ term, omitted square‑root) and correct them.

• Projector and screen
• PowerPoint slides with formula derivation and example
• Worksheet containing practice stars (luminosity & temperature)
• Scientific calculators (or calculator app)
• Printed Hertzsprung‑Russell diagram handout

Begin with a striking image of a red supergiant and ask students how we know its size without measuring it directly. Recall the previous lesson on black‑body radiation and introduce the success criteria: students will be able to compute a star’s radius using the Stefan–Boltzmann law.

1. Do‑Now (5'): Quick mental‑check – write the Stefan–Boltzmann equation and list its constants.
2. Mini‑lecture (10'): Derive the radius formula, emphasize the T⁴ term and unit conversion.
3. Guided practice (15'): Walk through the Sun example on the board, students follow on worksheets.
4. Independent practice (15'): Students calculate radii for three different stars from the table, using calculators.
5. Peer review (5'): Exchange worksheets, check each other's calculations against a solution key.
6. Concept check (5'): Whole‑class quiz using clickers – identify the most common pitfall in a given calculation.

Summarise how luminosity, temperature, and radius are linked and why accurate unit handling is crucial. Students complete an exit ticket: state one real‑world implication of knowing a star’s radius. Assign homework to research a star of their choice and compute its radius using the law.