Reflection and Refraction Basics

IGCSE Edexcel Physics
3.14-3.22 Light and Refraction
Key Concepts: Angle of incidence equals angle of reflection. $n = \sin i / \sin r$.

Section A: Reflection

1. State the two laws of reflection. [2]

Section B: Refraction

2. Light enters glass from air. Calculate $r$ when $i = 40^\circ$ and $n = 1.5$. [3]
3. Define the critical angle. [2]
4. Calculate critical angle for glass with $n = 1.5$. [2]
Total marks: 9

Mark Scheme

1. Incident ray, reflected ray and normal are coplanar; angle of incidence equals angle of reflection [2]
2. $\sin r = \sin 40^\circ / 1.5$; $r \approx 25.4^\circ$ [3]
3. Angle of incidence that gives $90^\circ$ refraction [2]
4. $\sin c = 1/1.5 = 0.667$; $c \approx 41.8^\circ$ [2]