1. Light

2. Early concepts of light Light has a dual nature, part particle and part wave. Right now will discuss only the wave nature of light. What_Is_Light_.asf The Speed of Light (c) c=3x10 8 m/s c= f It takes 8 minutes to travel from the sun to earth. If light could travel around earth, it would make 7.5 trips in one second. The distance light travels in one year is called a light year. The_Speed_of_Light.asf NOVA | scienceNOW | Lightning | PBS

3. Electromagnetic waves: wave that is partly electric and partly magnetic. They are transverse waves. Range of electromagnetic waves is called the electromagnetic spectrum Radio waves, microwaves, infrared, light, ultraviolet, x rays, gamma rays Electromagnetic_Waves.asf Putting_the_Electromagnetic_Spectrum_to_Use.asf Lowest frequency of light we see appears red; highest visible frequency appear violet

4. Light and transparent objects Light is produced by vibrating electric charges in atoms. Light passes through materials whose atoms are able to absorb the energy and immediately re-emit it as light. Glass and water are transparent to light. Opaque materials Materials that absorb light without re-emission, not allowing light through them. Wood, stone and people are opaque to light. Light energy is changed into random kinetic energy (internal energy).

5. Our atmosphere is transparent to visible light and some infrared but opaque to high frequency ultraviolet waves. Clouds are semitransparent to ultraviolet. Shadows A thin beam of light is called a ray. When light shines on an object, some of the rays may be stopped while others pass on in a straight-line path. A shadow is formed where light rays cannot reach. Umbra: a total shadow Penumbra: a partial shadow

6. Polarization Light travels in transverse waves A common light source emits light that vibrates in all directions (nonpolarized)

7. Light