Question: critical angle of an interface between a dense medium and air
[{'answer': 'angle of incidence', 'provenance': [{'wikipedia_id': '30426', 'title': 'Total internal reflection', 'start_paragraph_id': 2, 'start_character': 339, 'end_paragraph_id': 2, 'end_character': 357, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]