P3.2.2 Refraction of light

What is refraction?

• The change in direction of a light ray passing from one medium to another with a different optical density

  • Optically denser medium: light rays bend towards the normal, light travels slower

  • Optically less dense medium: light rays bend away from the normal, light travels faster

What is the refractive index?

• How much a medium can refract light

  • Higher refractive index slows down light more

State the three equations you can use to calculate refractive index

1. Using speed of light: speed of light in a vacuum (3×10⁸) / speed of light in a medium

2. Snell’s Law: n = sin (i) / sin (r) → you must know how to rearrange this 

3. Using critical angle: n = 1/sinC → you must know how to rearrange this

What are the conditions needed for total internal reflection to occur? 

1. Angle of incidence must be greater than critical angle

2. Light must travel from a more dense medium into a less dense medium

   • Light is always totally internally reflected in the denser medium

What is a critical angle?

• When the angle of refraction equals 90° (only 90 not more), the incident angle is called critical angle

Describe applications for total internal reflection

• Optical fibres: used in endoscopes and communication systems

• Periscopes