Total Internal Reflection

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  • Total Internal Reflection
    • Angle of reflection = angle of incidence
    • Optical Fibres
      • Work by bouncing waves off the sides of a thin inner core of glass or plastic
      • Very thin glass fibres that are designed to transmit light or infrared radiation
      • Waves enter one end of fibre and reflected repeatedly until it emerges at the other end
    • The angle of incidence is
      • Equal to the critical angle
        • Emerging ray comes out along the surface - quite a bit of internal reflection
      • Greater than the critical angle
        • No light comes out all internally reflected - total internal reflection
      • Less than the critical angle
        • Most of the light passes out, but little is interanlly reflected
      • Critical angle - angle of incidence of a lightray in a transparent substance that produces refraction along the boundary
    • Occurs when angle of incidence of a light ray in a transparent substance is greater than the critical angle
    • Endoscopes
      • Thin tube containing optical fibres that let surgeons examine inside the body
      • Image can be seen directly or by using a digital camera full - colour moving image on TV screen
      • 2 bundle sof optical fibres - one to carry light to the area and the other to carry an image back so it can be viewed
      • ADV = surgeons can now perform many operations by cutting small holes - keyhole surgery
    • Can only happen when a wave travels through a dense substance e.g. glass/ water towards a less dense substance like air
    • Value of critical angle depends on refrective index
      • Refractive index - 1/sin c ((critial angle)
      • Dense material, hig rereactive index, low critical index, total interanl reflection - move light

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