Foundation Year Program Waves 2 Geometrical Optics 1

Foundation Year Program Waves 2. Geometrical Optics 1 2015 -16

Foundation Year Program This lecture is on how light interacts with different objects. Basically, light is reflected, or refracted or dispersed as it changes materials. By the End, you should understand: • Laws of reflection • Refraction of light - refractive index and Snell’s law • Dispersion in prism • Total internal reflection and critical angle • Different lenses and their uses. 2 2015 -16

Foundation Year Program Reflection of light Learn the terms 3 2015 -16

Foundation Year Program Laws of Reflection 1. The normal to the surface of the mirror, the incident ray and the reflected ray lay all in the same plane. 2. The angle of incidence is equal to the angle of reflection: θ =θ i r 3. The angles are measured from the NORMAL, which is perpendicular to the surface. 4 2015 -16

Foundation Year Program Archimedes heat ray False or true? (Seminar activity) 5 2015 -16

Foundation Year Program Solar furnace 6 2015 -16

The Solar Project: A large number of mirrors to focus solar radiation Solar furnace Foundation Year Program The central tower can reach temperatures of 3, 500 °C and can melt salt or super heat steam for power generation. 7 2015 -16

Foundation Year Program How do we see color? White light coming from sun or other light What happens to the other colors? 8 2015 -16

Foundation Year Program Refraction of light Refraction is the change in direction of propagation of a wave due to a change in its transmission medium 9 2015 -16

Foundation Year Program Refraction of light Apparent position of fish (our eye assumes light ray is straight) Real position of fish 10 2015 -16

Foundation Year Program Refraction (video) https: //www. youtube. com/watch? v=uxq. Tvfb. Ti 4 k 11 2015 -16

Foundation Year Program Huygens principle Huygens's Principle states that every point on a wavefront is a source of wavelets, which spread forward. 12 2015 -16

Foundation Year Program The Index of Refraction The light changes direction (refracts) due to fact that light travels at a different speed in different media. The speed of light in any material is less than its speed in vacuum. This property of a medium is described by the absolute refractive index of the medium: 13 2015 -16

Foundation Year Program Snell’s Law If wave moves from medium 1 to medium 2: Relative refractive index: 14 2015 -16

Foundation Year Program Dispersion of light on prism If white light is incident on a glass prism it is dispersed; i. e. , it is split into all the visible colours – a continuous spectrum. Knowing that how would you explain that violet light bends more than red one? 15 2015 -16

Foundation Year Program Total Internal Reflection 16 2015 -16

Foundation Year Program Total Internal Reflection When rays pass from a medium of higher refractive index into one of lower refractive index at an angle greater than critical it reflects back into first medium 17 2015 -16

Foundation Year Program Application of Total Internal Reflection: Light travelling in optical fibres 18 2015 -16

Optical Lenses P=1/f Power of the lens Units: D (dioptre) are used by makers of eye-glasses Foundation Year Program Convex lens Concave lens 19 2015 -16

Foundation Year Program Optical Lens (convex) If a convex lens is held near an object, the object appears larger because the lens bends the light rays inward. The eyes trace the light rays back in straight lines and see a “virtual” image that is magnified. 20 2015 -16

Foundation Year Program Application of lenses Myopia (short-sighted) Hyperopia (long-sighted) Astigmatism 21 2015 -16

Foundation Year Program Single-lens reflex camera (SLR) 22 2015 -16

Foundation Year Program Application of lenses 23 2015 -16

Foundation Year Program What is happening? When you have small water droplets on your mobile screen, you see something strange. What causes this? 24 2015 -16

Foundation Year Program For the Seminar Think about places and things in your life where reflection and refraction, dispersion and total internal reflection are used. Come to the seminar ready to discuss these applications of geometric optics. 25 2015 -16

Foundation Year Program Assumptions Geometrical optics (ray optics) describes the propagation of light in terms of "rays" which travel in straight lines, and whose paths are governed by the laws of reflection and refraction at interfaces between different media. The assumptions of geometrical optics include that light rays: - propagate in rectilinear paths as they travel in a homogeneous medium - bend, and in particular circumstances may split in two, at the interface between two dissimilar media - follow curved paths in a medium in which the refractive index changes 26 - may be absorbed or reflected 2015 -16