This definitions covers Key Definitions within Reflection & Refraction for GCSE Physics. Revise Reflection & Refraction in Waves for GCSE Physics with 15 exam-style questions and 15 flashcards. This topic shows up very often in GCSE exams, so students should be able to explain it clearly, not just recognise the term. It is section 7 of 13 in this topic. Make sure you can use the exact wording confidently, because definition marks are often lost through vague language.
📖 Key Definitions
Normal: An imaginary line drawn perpendicular (at 90°) to a surface at the point where a ray meets it. All angles in optics are measured from the normal.
Angle of incidence: The angle between the incident (incoming) ray and the normal at the point of incidence.
Angle of reflection: The angle between the reflected ray and the normal. Always equals the angle of incidence.
Refraction: The change in direction of a wave as it passes from one medium to another, caused by a change in wave speed.
Critical angle: The angle of incidence (in the denser medium) at which the refracted ray travels along the boundary (angle of refraction = 90°). Beyond this, total internal reflection occurs.
Total internal reflection (TIR): Complete reflection of a wave at a boundary when the angle of incidence exceeds the critical angle, with no refraction into the less dense medium.
Practice questions for Reflection & Refraction
According to the law of reflection, the angle of incidence is:
Explain why a ray of light bends when it passes from air into water.