PhysicsMate: A Curriculum-Grounded Bengali Benchmark for Secondary Physics QA with Small-Model Adaptation

This paper presents PhysicsMate, the first curriculum-grounded Bengali physics QA benchmark and multi-relational knowledge graph (1,760 nodes, 2,600 edges across 10 ontological types, and 1,834 QA pairs) derived from the NCTB Grade 9–10 syllabus. We conduct a controlled LoRA adaptation study across three small language model scales (Qwen3 0.6B, 1.7B, and 4B), demonstrating monotonic capacity-dependent closed-book accuracy gains (+5.5, +15.0, and +23.3 percentage points) and enabling offline 4-bit edge deployment. Finally, an ontological diagnostic analysis reveals that adaptation primarily aids structured curricular categories (physical quantities: +93.9%, named laws: +56.6%) while pinpointing remaining gaps in entity-level reasoning.