A full, ready-to-teach 13-slide Power point lesson on Two-Source Interference and Young’s Double-Slit Experiment, designed for AS Level / Cambridge International (CIE) Physics, topic 8.3. What’s included: Starter recall task on stationary waves (nodes/antinodes) Clear learning objectives and “I Can” success criteria The four conditions for observable interference fringes (coherence, same frequency, similar amplitude, same plane of polarisation) Constructive vs destructive interference explained through path difference Derivation and explanation of the fringe spacing formula λ = ax/D A fully worked CIE board-style numerical example (fringe spacing + counting fringes) Group challenge task (predict/explain, calculate, analyse — differentiated for pair/group work) Quick-fire mini plenary with model answers Tiered Core/Extension/Mastery success criteria for differentiation Full plenary with self-assessment checklist and exit ticket Embedded video link to a double-slit demonstration How to use it: Ideal for a single 60-75 minute AS/A Level lesson, or split across two shorter periods. Works well for CIE, but conditions and formula transfer directly to Edexcel/AQA/OCR A-Level and IB Physics interference topics too, with minor tweaks to exam-board wording. Suitable for: AS Level Physics, A-Level Physics (Year 12), IGCSE Extension/Further Physics extension work, IB DP Physics SL/HL.