DAILY QUESTION March 17, How do rainbows form?

Agenda3/17/09  Daily Question  Ch 15-4 Notes  Brain Pop: “Rainbows” Assignments: Worksheet due 3/18

Light  Light travels in a straight line through empty space.  When light waves pass from one medium to another they bend, or refract

Light  When light moves from a material in which its speed is higher to a material in which its speed is lower  The ray is bent toward the normal (Fig. 28A)  When light moves from a material in which its speed is lower to a material in which its speed is higher  The ray is bent away from the normal (Fig. 28B)

Refraction  Makes objects appear to be in different positions  Fish in water  The misplaced images are virtual images like the images that form in a mirror.

Mirage  A virtual image caused by refraction of light in the atmosphere  Seeing the image of the sky on the road, your mind assumes that there is water on the road causing a reflection of the sky

 If the angle at which light rays meet the boundary between two mediums becomes small enough:  The rays will be reflected as if the boundary were a mirror.  This angle is called the critical angle.  This type of reflection is called total internal reflection.

Fiber Optics  Use total internal reflection  Made by fusing bundles of transparent fibers together.  Light inside a fiber bounces off the walls due to total internal reflection.  Used for surgical procedures, transmit computer data and telephone signals

Lenses rely on refraction  Converging lenses  Bends light inward  Can create either a virtual image or real image  Example: Magnifying glasses  Diverging lenses  Bends light outward  Can only create a virtual image

Lenses can magnify images  Magnification is any change in the size of an image compared with the size of the object  Usually produces an image larger than the object  A compound microscope uses multiple lenses to provide greater magnification

Prisms  Can separate white light into its component colors  Different colors of light are refracted differently

In the visible spectrum: When light travels through a medium, the wavelength impacts the speed of light  R- red – fastest speed, refracts the least  O- orange  Y- yellow  G- green  B- blue  I- indigo  V- violet – slowest speed, refracts the most

Dispersion  The effect in which light separates into different colors because of differences in wave speed  Example: RAINBOWS!