Lesson 27

Core outcomes Learners calculate magnification, rearrange formulae, plot paired data, determine slope and intercept, and interpret results in an astronomical context.
Suggested teaching sequence Starter recap → modelled magnification examples → guided equation practice → graphing task → plenary skill check. Use the 60-minute route by selecting key questions; use the full sequence for a 90-minute lesson.
Resources and preparation Calculators, rulers, graph paper or pre-printed axes, formula sheet, worked-example display and optional telescope or eyepiece images. Prepare differentiated question sets and keep answers available for self- or peer-marking.
Prior knowledge Basic substitution, inverse operations, units, coordinates and the purpose of telescopes. Briefly revisit focal length before introducing magnification.
Assessment opportunities Check rearrangement during the starter, question learners on units during worked examples, review graph axes and scales before plotting, and use the plenary to identify misconceptions for follow-up.
Key misconceptions Mixing focal-length units; reversing objective and eyepiece focal lengths; treating magnification as having units; confusing slope with intercept; and assuming greater magnification always produces a better image.
Differentiation Support with formula triangles, worked steps, pre-labelled axes and paired practice. Extend by asking learners to justify whether answers are reasonable, derive an unknown before substitution, or interpret the physical meaning of a graph’s slope.
Success indicators Learners select the correct formula, show substitutions clearly, retain consistent units, plot accurately, calculate a gradient from two suitable points and explain what the result represents.