Total Internal Reflection

Total Internal Reflectionvideo

Total Internal Reflection

• Sometimes, when light is moving from a denser medium towards a less dense one, instead of being refracted, all of the light is reflected

  • This phenomenon is called total internal reflection

• Total internal reflection (TIR) occurs when:

  The angle of incidence is greater than the critical angle and the incident material is denser than the second material

• Therefore, the two conditions for total internal reflection are:

  • The angle of incidence > the critical angle

  • The incident material is denser than the second material

Critical Angle and TIR

TIR occurs when the angle of incidence is greater than the angle of reflection

• Total internal reflection is utilised in:

  • Optical fibres e.g. endoscopes

  • Prisms e.g. periscopes

Prisms

• Prisms are used in a variety of optical instruments, including:

  • Periscopes

  • Binoculars

  • Telescopes

  • Cameras

   

• They are also used in safety reflectors for bicycles and cars, as well as posts marking the side or edge of roads

   

• A periscope is a device that can be used to see over tall objects

  • It consists of two right-angled prisms

Reflection of light through a periscope

• The light totally internally reflects in both prisms

Internal Reflection in Prisms

Single and double reflection through right-angled prisms

Refractive Index & Critical Angle Equation

Refractive Index & Critical Angle Equation

• The critical angle, c, of a material is related to its refractive index, n

• The relationship between the two quantities is given by the equation:

$\sin c = \frac{1}{n}$

• This can also be rearranged to calculate the refractive index, n:

$n = \frac{1}{\sin c}$

• This equation shows that:

  • The larger the refractive index of a material, the smaller the critical angle

  • Light rays inside a material with a high refractive index are more likely to be totally internally reflected

Optical Fibres

Optical Fibres

• Total internal reflection is used to reflect light along optical fibres, meaning they can be used for

  • Communications

  • Endoscopes

  • Decorative lamps

• Light travelling down an optical fibre is totally internally reflected each time it hits the edge of the fibre

• This means information can be transmitted over long distances with minimal loss

Total Internal Reflection in an Optical Fibre

Optical fibres utilise total internal reflection for communications

• Optical fibres are also used in medicine in order to see within the human body

Optical Fibres in Medicine

Endoscopes utilise total internal reflection to see inside a patient's body