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1. Total Internal reflection and critical angle Chapter 14:Refraction Lesson 3

2. What is Refractive Index? The refractive index of a medium is defined as the ratio of the velocity of light in a vacuum to the velocity of light in the medium. A ray of light travels more slowly in an optically dense medium than in one that is less dense.

3. What is Refraction? When a ray is incident on the interface between two dielectrics of differing refractive indices (e.g. glass–air), refraction occurs

4. As the angle of incidence Increases , the angle of refraction Increases .

5. Watch the video clip https://www.youtube.com/watch?v=T-iy29oEmSI What is the difference between critical angle and total angle of reflection??

6. What is Critical Angle? At a certain angle, the refracted ray follows a path exactly along the surface of the dense medium. When the angle of refraction is at 90° the incident angle is called the “ Critical Angle”

7. What is Total Internal Reflection (TIR)? If the incident ray is increased beyond the critical angle, the light is no longer refracted • Instead, it is reflected back inside the medium • This is called “ total internal reflection”

8. Total Internal Reflection A light ray hits the inside face of a semicircular block.

9. Total Internal Reflection

10. Conditions for TIR & Critical Angle Light is travelling slower in the first medium than in the second medium (v1 < v2) Thus light is moving from medium of higher refractive index to one of lower refractive index (n1 > n2) Critical angle (C) is defined when the angle of refraction is 90° to the normal (θ2 = 90°) TIR occurs when angle of incidence is larger than the critical angle ( θ 1 > C)

11. Calculating Critical Angle

12. Critical angles of different materials Medium Refractive Index Critical Angle Glass 1.50–1.70 30°–42° Water 1.33 49° Perspex 1.5 42° Diamond 2.42 24°

13. Applications of TIR TIR in Fiber Optics Communication Endoscopes TIR in Prism Periscopes Binoculars Single Lens Camera Retro Reflectors

14. Dispersion and the Rainbow The index of refraction varies slightly with the frequency of light; in general, the higher the frequency, the higher the index of refraction. This means that refracted light is “spread out” in a rainbow of colors; this phenomenon is known as dispersion.

15. Dispersion and the Rainbow Rainbows are created by the dispersion of light as it refracts in a rain drop.

16. Dispersion and the Rainbow As the drop falls, all the colors of the rainbow arrive at the eye.

17. Dispersion and the Rainbow Sometimes a faint secondary arc can be seen.

18. Aberration occurs when the incident light fails to focus at a single point. The aberration types are: Monochromatic aberrations (can be produced with a single wavelength of light): Spherical Aberration Coma Oblique Astigmatism Power Error (Field Curvature) Distortion Chromatic aberration (occur only with polychromatic light). 18 Aberration

19. Monochromatic aberrations They called monochromatic aberrations, since they occur independently of color. The 5 Seidel aberrations are spherical aberration, coma, oblique astigmatism, curvature of field (power error), and distortion. Peripheral rays Peripheral rays are those that enter the lens nearer the edge of the lens. Paraxial rays are those that pass through the central area of the lens. 19

20. Chromatic Aberration Transverse (Lateral) 20 Longitudinal (Axial) The failure of a lens to focus all colours in the same plane is known as chromatic aberration.

21. Thank You!