1. Intro to Light Chapter 27 27.1 & 27.3 Notes

2. What is light? The only thing you can see—all objects either emit or reflect light Most objects you see reflect light from some other source. If you remove the light source, the object cannot be seen. However some objects can also produce their own light (fire, light bulbs).

3. Early Concepts of Light Some ancient Greek philosophers thought that light consisted of tiny particles, which would enter the eye to create the sensation of vision Others, like Socrates and Plato, believed that vision resulted from streamers or filaments emitted by the eye making contact with an object

4. Early Concepts of Light A Greek scientist, Empedocles, and a Dutch scientist, Christian Huygens, argued that light acts as a wave The wave theory was accepted in the nineteenth century In 1905, Einstein published a theory explaining the photoelectric effect Light consists of tiny particles called photons Photons are bundles of concentrated electromagnetic energy that have no mass Scientists now argue that light has a dual nature; it acts as both a particle and a wave

5. Electromagnetic Waves The electromagnetic spectrum consists of radio waves, microwaves, infrared, light, ultraviolet rays, X-rays, and gamma rays Light is energy that is emitted by accelerating electric charges—often electrons in atoms This energy travels in a wave that is partly electric and partly magnetic—known as an electromagnetic wave

6. Electromagnetic Waves Light is a portion of the family of electromagnetic waves that includes radio waves, microwaves, and X-rays. The range of electromagnetic waves is called the electromagnetic spectrum

7. Frequency and Wavelength of Light Frequency of light corresponds to color Visible light: what we can see, spectrum goes from red (lowest frequency) to violet (highest frequency) Electromagnetic waves of frequencies lower than the red of visible light are called infrared Electromagnetic waves of frequencies higher than those of violet are called ultraviolet The colors of the visible light spectrum follow the order: ROY G BIV Red orange yellow green blue (indigo) violet

8. What are infrared and ultraviolet used for? Ultraviolet lights are used as black lights, to sterilize things, and are used in tanning beds Infrared are used as warmers (heat lamps) and for thermometers (infrared cameras) They are both invisible to the naked eye. Both lights also have visible light mixed in so you know it is on

9. The EM spectrum 10 4 10 6 10 8 10 10 10 12 10 14 10 16 10 18 10 20 10 22 10 24 Frequency Hz Wavelength (m) 10 4 10 2 1 10 -2 10 -4 10 -6 10 -8 10 -10 10 -12 10 -14 Visible Light Radio Waves Microwaves Infrared Ultraviolet X-rays Gamma Rays