Optics: Reflection, Refraction Mirrors and Lenses 05/25/2006 Optics Mirrors and Lenses Lecture 16

Light Light can be a wave or a particle. UCSD: Physics 8; 2006 Light Light can be a wave or a particle. Individual particles of light are called photons. Photons have no mass, they are a bundle of energy. The higher the frequency the greater the wave has.

UCSD: Physics 8; 2006 Light Intensity Intensity is the the amount of light covering a given surface area. Intensity is a measure of power, so it is the amount of power over a certain amount of space. As light gets further away it spreads out more, which means the amount of power on a given area is less and there fore the intensity is less. (don’t worry I am not making you do the math here) Spring 2006

Light Intensity Spring 2006

Optics: Reflection, Refraction 05/25/2006 Reflection We describe the path of light as straight-line rays Reflection off a flat surface follows a simple rule: angle in (incidence) equals angle out (reflection) angles measured from surface “normal” (perpendicular) surface normal same angle exit ray reflected ray incident ray Lecture 16

Reflection Vocabulary Real Image – Image is made from “real” light rays that converge at a real focal point so the image is REAL Can be projected onto a screen because light actually passes through the point where the image appears Always inverted

Reflection Vocabulary Virtual Image– “Not Real” because it cannot be projected Image only seems to be there!

Optics: Reflection, Refraction 05/25/2006 Hall Mirror Useful to think in terms of images “real” you “image” you mirror only needs to be half as high as you are tall. Your image will be twice as far from you as the mirror. Lecture 16

LEFT- RIGHT REVERSAL AMBULANCE

Optics: Reflection, Refraction 05/25/2006 Curved mirrors What if the mirror isn’t flat? light still follows the same rules, with local surface normal Parabolic mirrors have exact focus used in telescopes, backyard satellite dishes, etc. also forms virtual image Lecture 16

Two types of curved mirrors UCSD: Physics 8; 2006 Two types of curved mirrors Convex: Means the mirrors surface bulges outward. Rays are reflected away from the center. Spring 2006

Two types of curved mirrors UCSD: Physics 8; 2006 Two types of curved mirrors Concave: Means the mirrors surface curves inwards. Rays are focused towards a middle point. Spring 2006

Parts of the mirror image UCSD: Physics 8; 2006 Parts of the mirror image We can see an image where the rays meet. This is called a focal point. The distance from the mirror surface to the focal point is called the focal length. For convex mirrors the image is virtual. For concave mirrors the image is real. Spring 2006

UCSD: Physics 8; 2006 Curved Mirrors The line running perpendicular through the middle of the mirror is called the principal axis. If we were to make a complete circle for the mirror the very center of the circle would be at “C” (center of curvature) Spring 2006

UCSD: Physics 8; 2006 Objects in mirrors Where you place an object relative to a mirror determines the following: Is the image real or virtual Is the image larger or smaller than the true object. Is the image inverted (up side down) or up right. Spring 2006

Optics: Reflection, Refraction For a real object between f and the mirror, a virtual image is formed behind the mirror. The position of the image is found by tracing the reflected rays back behind the mirror to where they meet. The image is upright and larger than the object. Optics: Reflection, Refraction 05/25/2006 For a real object between f and the mirror, a virtual image is formed behind the mirror. The image is upright and larger than the object. Lecture 16

Optics: Reflection, Refraction For a real object between f and the mirror, a virtual image is formed behind the mirror. The position of the image is found by tracing the reflected rays back behind the mirror to where they meet. The image is upright and larger than the object. For a real object between C and f, a real image is formed outside of C. The image is inverted and larger than the object. For a real object close to the mirror but outside of the center of curvature, the real image is formed between C and f. The image is inverted and smaller than the object. Optics: Reflection, Refraction 05/25/2006 For a real object between C and f, a real image is formed outside of C. The image is inverted and larger than the object. Lecture 16

Optics: Reflection, Refraction For a real object between f and the mirror, a virtual image is formed behind the mirror. The position of the image is found by tracing the reflected rays back behind the mirror to where they meet. The image is upright and larger than the object. For a real object between C and f, a real image is formed outside of C. The image is inverted and larger than the object. For a real object at C, the real image is formed at C. The image is inverted and the same size as the object. For a real object close to the mirror but outside of the center of curvature, the real image is formed between C and f. The image is inverted and smaller than the object. Optics: Reflection, Refraction 05/25/2006 For a real object at C, the real image is formed at C. The image is inverted and the same size as the object. Lecture 16

Optics: Reflection, Refraction For a real object between f and the mirror, a virtual image is formed behind the mirror. The position of the image is found by tracing the reflected rays back behind the mirror to where they meet. The image is upright and larger than the object. For a real object close to the mirror but outside of the center of curvature, the real image is formed between C and f. The image is inverted and smaller than the object. Optics: Reflection, Refraction 05/25/2006 For a real object close to the mirror but outside of the center of curvature, the real image is formed between C and f. The image is inverted and smaller than the object. Lecture 16

Optics: Reflection, Refraction For a real object at f, no image is formed. The reflected rays are parallel and never converge. Optics: Reflection, Refraction 05/25/2006 For a real object at f, no image is formed. The reflected rays are parallel and never converge. Lecture 16

UCSD: Physics 8; 2006 Convex Mirrors No matter where I place an object in front of a convex mirror The image will always be inside (behind) the mirror.

UCSD: Physics 8; 2006 Mirror Equation We can use math to determine focal length and magnification. Mirror Equation: 1/f = 1/di + 1/do f = focal length, di = distance to image do = ditsance to object Spring 2006

Magnification You can find out by how much the image was enlarged or UCSD: Physics 8; 2006 Magnification You can find out by how much the image was enlarged or Shrunk by simply comparing the two heights. Magnification = hi / ho It also happens to be the same as –di / do Spring 2006

UCSD: Physics 8; 2006 Practice Problem An object is placed 12 cm form a mirror and the image appears 20 cm away. What is the focal length? An image appears at a distance of 14m and the mirror has a Focal length of 10m. How far is the object from the mirror? Spring 2006

Optics: Reflection, Refraction 05/25/2006 Refraction Light also goes through some things glass, water, eyeball, air The presence of material slows light’s progress interactions with electrical properties of atoms. The “light slowing factor” is called the index of refraction Light bends at interface between refractive indices bends more the larger the difference in refractive index n2 = 1.5 n1 = 1.0 A B Lecture 16

Convex Lenses Thicker in the center than edges. Lens that converges (brings together) light rays. Forms real images and virtual images depending on position of the object. A real image is inverted and smaller. Virtual is larger and upright. The Magnifier

Concave Lenses Lenses that are thicker at the edges and thinner in the center. Diverges light rays All images are upright and smaller. The De-Magnifier

Lens Equations The lens equation is the exact same as the mirror equation. 1/f = 1/di + 1/do The magnification equation is the same too. m = hi / h0