Reflection and refraction describe how light behaves when it meets a boundary between different materials, and both concepts are heavily tested in the IGCSE Physics optics section through diagrams and calculations.
1. The Law of Reflection
The law of reflection states that the angle of incidence equals the angle of reflection, both measured from the normal, an imaginary line perpendicular to the reflecting surface. This law applies to all reflecting surfaces, including plane mirrors.
2. Understanding Refraction
Refraction occurs when light changes speed as it passes from one medium to another, causing it to bend at the boundary. Light bends towards the normal when entering a denser medium and away from the normal when entering a less dense medium.
3. Refractive Index
The refractive index of a material measures how much it slows down and bends light, calculated using n = sin(i)/sin(r), where i is the angle of incidence and r is the angle of refraction. A higher refractive index means light bends more and travels more slowly through that material.
4. Total Internal Reflection
Total internal reflection occurs when light travelling from a denser to a less dense medium hits the boundary at an angle greater than the critical angle, causing all the light to reflect back rather than refract. This principle is the basis for how optical fibres transmit data.
Frequently Asked Questions
What is the normal in reflection and refraction diagrams?
The normal is an imaginary line drawn perpendicular to a surface at the point where a light ray meets it, used as a reference for measuring angles.
What causes total internal reflection?
Total internal reflection occurs when light travels from a denser to a less dense medium at an angle greater than the critical angle, causing it to fully reflect instead of refract.
Conclusion
Practising ray diagrams alongside the relevant formulas is the most effective way to become confident with reflection and refraction questions in the IGCSE exam.