Refraction, refractive index and ray paths

≈ 48 min

Refraction, refractive index and ray paths

Refraction is a change in direction caused by a change in wave speed when light crosses a boundary at an angle. Light entering a medium with a higher refractive index slows and bends toward the normal; leaving it for a lower-index medium, it speeds up and bends away from the normal. Angles in Snell's law are measured between the ray and the normal, not between the ray and the surface. The refractive index can be expressed as n = c/v, where c is light speed in vacuum and v is speed in the material. A ray diagram needs a boundary, normal, arrows and correctly placed angles.

Work it through

If light travels through glass at 2.0 × 10⁸ m s⁻¹, n = c/v = 3.0 × 10⁸ / 2.0 × 10⁸ = 1.5. A ray entering the glass from air must bend toward the normal because it slows. The result n > 1 is a reasonableness check: ordinary transparent materials have light speeds below c.

Mastery target

Draw and explain a refracted ray, calculate refractive index or apply Snell's law with angles measured from the normal.

When light enters glass from air, it usually bends:

Toward the normal

Away from the normal

Along the boundary only

Without changing speed

Name the key physics term from Refraction, refractive index and ray paths that best fits the explanation and visual model.

Calculate n for light travelling at 2.0 × 10⁸ m s⁻¹ in a material. Use c = 3.0 × 10⁸ m s⁻¹.

Which statement corrects a common misunderstanding in Refraction, refractive index and ray paths?

Correct: The normal is an imaginary line perpendicular to the boundary. It is the reference for incidence and refraction angles, not the surface itself.

A diagram or formula can be used without naming the system, direction or condition.

A measured pattern always proves one cause with no uncertainty or alternative explanation.

Units can be ignored if the numerical answer looks familiar.