Refraction, Snell's Law and Total Internal Reflection

Identify denser and rarer media; confirm light travels denser to rarer; apply sin theta_c = n2/n1; compare the given incidence angle with theta_c; state whether refraction or TIR occurs.

Diagram should show interface, normal, incident ray in denser medium, refracted ray bending away from normal, critical-angle case with refracted ray along interface, and TIR case with reflected ray inside the denser medium.

A common wrong answer is sin theta_c = n1/n2, which can give a value greater than 1 and is physically impossible.

Refraction is the bending of light when it passes obliquely from one transparent medium to another because its speed changes. Total internal reflection is the complete reflection of light back into a denser medium when the angle of incidence exceeds the critical angle.

Refraction is the bending of light when it passes obliquely from one transparent medium to another because its speed changes. Total internal reflection is the complete reflection of light back into a denser medium when the angle of incidence exceeds the critical angle. Snell's law: n1 sin theta1 = n2 sin theta2. Critical angle for denser medium 1 to rarer medium 2: sin theta_c = n2/n1, where n1 > n2. Refractive index is dimensionless; angles are measured from the normal, not from the surface. In an optical fibre, light repeatedly undergoes total internal reflection inside the core, allowing signals to travel along curved paths with low loss.

Snell's law connects the angles of incidence and refraction with the refractive indices of the two media. When light travels from a denser medium to a rarer medium, the refracted ray bends away from the normal. At the critical angle, the refracted ray grazes the interface. For angles greater than the critical angle, no refracted ray emerges and total internal reflection occurs. This explains optical fibres, sparkling of diamonds and mirage-like effects at school level. Snell's law: n1 sin theta1 = n2 sin theta2. Critical angle for denser medium 1 to rarer medium 2: sin theta_c = n2/n1, where n1 > n2. Refractive index is dimensionless; angles are measured from the normal, not from the surface. Light travels from glass of refractive index 1.5 to air of refractive index 1.0. sin theta_c = n2/n1 = 1.0/1.5 = 0.667. Therefore theta_c is about 41.8 degrees. If the incidence angle in glass is 50 degrees, total internal reflection occurs because 50 degrees is greater than 41.8 degrees. Questions ask for critical angle calculation, conditions for TIR, optical fibre working, and comparison between ordinary reflection and total internal reflection. A common wrong answer is sin theta_c = n1/n2, which can give a value greater than 1 and is physically impossible.