Day 9 5.19.11 Topic: What is Light? Objective: I will describe the properties of light and compare the speed of light and sound. Science Starter: Image you are sitting at a table with a red apple in front of you. Your friend closes the door and turns off the lights. It is totally dark in the room, there is no light. Which statement best describes how you see the apple?

Science Starter: Image you are sitting at a table with a red apple in front of you. Your friend closes the door and turns off the lights. It is totally dark in the room, there is no light. Which statement best describes how you see the apple? A. You will not see the red apple, regardless of how long you are in the room B. You will see the red apple after your eyes have had time to adjust to the darkness C. You will see the apple after your eyes have adjusted but you will not see the red color. D. You will see only the shadow of the apple after your eyes have had time to adjust E. You will see only a faint outline of the apple after your eyes have adjusted to the darkness

5 Properties of Light: From the video clip, “What is light?” list at least 5 properties of light: 1. 2. 3. 4. 5.

Illustration: Draw a diagram that illustrates how you are able to see a page of a book. (Hint: trace the path of light from the source to your eyes).

How is light produced? Light is produced primarily as atoms absorb and emit energy in tiny bundles called photons. Incandescent light: produces light as electricity is passed through a thin wire (filament) producing heat and emitting light. Since most of the energy is converted to heat, this is a very inefficient method of producing light. Fluorescent light: electricity causes atoms to produce ultraviolet (UV) light which is absorbed by the white coating and emitted as white light. Fluorescent light is 4 times more efficient than incandescent light.

Incandescent v. Fluorescent

Speed of light: Light travels much faster than sound: Sound: 340 m/sec Light: 3 x 108 m/sec ( 186,000 miles/sec) Speed of light has its own symbol: c c= speed of light= 3x108 m/sec Comparison of speed of light and sound with lightning: When you see lightning, count the # of seconds before you hear the thunder. Each second equates to roughly 1/5 mile. That’s 3 million Football fields in One second

Summary

Reflection: How is an incandescent bulb different from a fluorescent bulb? Why do we hear lightning before we hear thunder?