Objectives: Recognize that light is the visible portion of an entire range of electromagnetic frequencies. Describe the ray model of light Solve problems involving the speed of light Solve illumination problems Explain the formation of color by light and by pigments and dyes

Chapter 16 Light

16.1 Light Fundamentals The facts of Light –The visible spectrum is a very small portion of the electromagnetic spectrum –The straight line path of light has led to the RAY MODEL of light.

The Speed of Light –Galileo was first to hypothesize that light has a finite speed –Ole Roemer was the first to determine that light does travel with a measurable speed. –American Albert A. Michelson developed an Earth-based technique to measure the speed of light. He became the first American to receive the Nobel prize in science. –The speed of light is defined to be exactly 299,792,458 m/s. –3.00 X 10 8 m/s is sufficient for calculations.

Source of Light –A LUMINOUS body emits light –An ILLUMINATED body reflects light. –LUMINOUS FLUX, P is the rate at which visible light is emitted from a source. The unit is the lumen (lm). P = 4π(l) where l is the luminous intensity P = 4π(l) where l is the luminous intensity –The illumination of a surface is called the ILLUMINANCE (E) and is measured in lux, (lx). –A surface illuminated by a luminous body obeys the inverse-square relationship.

–Luminous intensity (l) of a point source is the luminous flux that falls on a 1 m 2 of a sphere 1 m in radius. The unit for luminous intensity is the candela (cd). –There are two ways to increase the illumination of a surface: Move the surface closer Use a brighter bulb. Illuminance E = P / 4πd 2

16.2 light and Matter Transparent, translucent, and opaque materials Color –Newton called the ordered arrangement of colors from violet to red a spectrum. –Each color in the spectrum is associated with a specific wavelength of light.

–Color by addition: White light can be formed from colored light. Red, green, and blue are called the primary colors Yellow, cyan, and magenta are the secondary colors Complementary colors combine to form white light.

–Color by subtraction: A dye is a molecule that absorbs certain wavelengths of light and transmits or reflects others. A pigment is like a dye in that it absorbs certain colors and reflects or transmits others. The primary pigments are yellow, cyan and magenta. The secondary pigments are blue, green and red.

Formation of Color in thin films –The separation of white light into the spectrum of colors is due to destructive interference of light waves, or thin-film interference. Polarization of Light –Ordinary light contains electromagnetic waves vibrating in every direction perpendicular to its direction of travel. Each wave can be broken down into two perpendicular components.

The Ray and Wave Models of Light –Both models are needed to explain the behavior of light in different settings.