Refraction

Summary

Refraction is the change in direction of a wave as it passes from one medium to another, commonly observed with light, sound, and water waves. Refraction allows for optical instruments like lenses and prisms and is key to focusing light on the retina.

• Refraction — change in the direction of a wave passing from one medium to another. Example: Light bending when it enters water from air.
• Refractive Index — ratio of the speed of light in a vacuum to its speed in a medium. Example: Light slows down and bends towards the normal when entering glass.
• Total Internal Reflection — occurs when the angle of incidence is greater than the critical angle, and the incident material is denser than the second material. Example: Light staying inside an optical fibre.
• Dispersion — splitting of white light into its component colors. Example: A prism creating a spectrum of colors from white light.

Exam Tips

Key Definitions to Remember

• Refraction: Change in direction of a wave passing from one medium to another.
• Refractive Index: Ratio of speed of light in a vacuum to speed in a medium.
• Total Internal Reflection: Occurs when light is completely reflected within a denser medium.
• Dispersion: Splitting of white light into different colors.

Common Confusions

• Thinking light always bends away from the normal when entering a denser medium.
• Confusing refraction with reflection.

Typical Exam Questions

• What happens to light when it passes from air into water? It slows down and bends towards the normal.
• How does a prism create a spectrum of colors? By dispersing white light into its component colors.
• What is the critical angle? The angle of incidence at which light is refracted along the boundary.

What Examiners Usually Test

• Understanding of how refraction affects light direction and speed.
• Ability to explain total internal reflection and its applications.
• Knowledge of how dispersion occurs and its effects on light.