Chapter 26 Geometrical Optics
Outline 26-1 The Reflection of Light 26-2 Forming Images with a Plane Mirror 26-3 Spherical Mirror 26-4 Ray Tracing and the Mirror Equation 26-5 The Refraction of Light 26-6 Ray Tracing for Lens 26-7ThiL7 Thin Lens Equa tion 26-1 The Reflection of Light
Light propagation can be described in terms of “wave front” and “rays”. Wave front is mostly associated with physical optics (difficult to understand), while rays are mostly associated with geometrical optics (easy to understand).
Wave front: Think about water wave!
Figure 26-1 Wave Fronts and Rays of a point light source • The rays are always traveling in straight line and they indicate the traveling direction of the light--- in Geometrical Optics! • Rays are always at right angle to the wave fronts.
More wave fronts
Figure 26-2 Spherical (point source light) and Planar (sun light) Wave Fronts In ggpeometrical optics,,y a few rays are used for the representation of the light traveling.
The Law of Reflection
Figure 26-3 Reflection from a Smooth Surface The Law of Reflection
θr = θi
The angle of reflection is equal to the angle of incidence (Fig 26-3). The applications of Reflection Law • Reflection on smooth surface (figure a): Specular reflection. • Reflection on rough surface (figure b): Diffuse reflection.
Figure 26-4 Reflection from Smooth and Rough Surfaces 26-2 Forming Images with a Plane Mirror
Imaging process of the human eye: The imaging process of human is a point – to – point matching process between the distant object and the retina image, in which the image is focused by the eye “lens on the retina for sensing.
Figure 27-1 Basic Elements of the Human Eye The imaging process of a flat mirror: application of Reflection Law The point P of the object is propagate according to the Reflection Law. To the observer/eye, it appears that the rays are coming from point P′ behind the mirror.
We can verify that the image and the object is the same height (1:1 image), and is in the same distance from the mirror (See Fig. B).
Figure 26-6 Locating a Mirror Image Summaryygg of Flat/Plane Mirror imaging
• 1:1 object-to-image, upright. • Left and right is inversed to the observer. • The eye/ ob server see a vi r tual image be hin d the m irror.
A flat mirror has no optical power, and it only changes the direction of light traveling ! Example 26-1 An observer is at table level, a distant d to the left of a flower of height h. The flower itself is a distance d to the left of a mirror, as shown in the sketch. Find y in terms of the height of the flower h.
d
Example 26-1 Reflecting on a Flower
Two mirrors are placed at right angles. Two mirrors are placed at right angles. An incident ray of light makes an angle of 30º with the x axis and reflects from the lower mirror. Find the angle the outgoing ray makes with the y axis after it reflects once from each mirror. Summary
26-1 The Reflection of Light “Wave front” and “rays”. Light travels along the rays, and is vertical to the wave-front. The Law of Reflection
θr = θi
26-2 Forming Images with a Plane Mirror • 1:1 imaging. • virtual image.
-- Application of the Reflection law: Flat mirror only changes the tra veling direction of a ra y.