- Discuss and review how light travels and how it interacts with matter - Study the nature of shadows and learn what conditions are necessary to form them - Investigate the differences between point and extended light sources TODAY’S OUTCOMES: BEHAVIOR OF LIGHT

13. Set up the light station so that it illuminates the screen. Predict what you will observe when you place the mask over the aperture (with the hole positioned so that light can go through it). 14. Then try the experiment. What do you observe? Most predicted a small spot, just as was observed with the two small light bulbs. Answers may vary, according to the positioning of the mask and light box. A pattern resembling a “blurry V” or a “heart” appeared on the screen. 15. Repeat activity 13-14, using a mask with a very small hole in it. What do you observe? A much sharper pattern appeared, resembling a “V”, this time with a much sharper definition. 16. Explain the shapes seen on the screen in activities 14 and 15. A hint: look at the filament of the light station light bulb, using the “filament viewer” (a disk of translucent plastic). Using the “filament viewer”, one can see that the filament has a shape of an inverted “V”. Thus, the source of the light is not a small point, but rather an source with some shape. This principle will be investigated further in today’s activity!

The source of light doesn’t matter - it always travels in a straight line! LIGHT TRAVELS IN STRAIGHT LINES laser This is obvious with a laser

The source of light doesn’t matter - it always travels in a straight line! LIGHT TRAVELS IN STRAIGHT LINES Not as obvious with a light bulb - light is emitted in ALL directions mask limits light to a narrow beam small light bulb

The size of the spot on the screen depended on the distances LIGHT TRAVELS IN STRAIGHT LINES light bulb gets closer, spot on the screen grows larger Is this consistent with the observation that light beams follow straight lines? YES

Small light bulb vs. large light bulb - how were they different? DIFFERENT LIGHT BULBS vs. In the small bulb, the light given off in a particular direction comes from a very small “point” In a large bulb, the light in a particular direction comes from every possible point on the filament KEEP THIS IN MIND AS YOU DO TODAY’S ACTIVITY!

You reviewed some new operational terms: INTERACTION OF LIGHT WITH MATTER Transparent: light passes through “unaffected”, as a beam Translucent: light passes through, but is dimmer and scattered in many directions Opaque: light cannot pass through THINK: Were some of the materials you looked at difficult to classify? Were any truly transparent or opaque?

You reviewed some new operational terms: INTERACTION OF LIGHT WITH MATTER Absorption: light stops in the object Reflection: light bounces off the material. (If it is no longer a beam, it is called diffuse reflection.) THINK: Were some of the opaque materials you looked at difficult to classify? Were any 100% absorptive or reflective?

- Light travels in a straight line (and observations that demonstrate this fact!) - Definitions: - transparency - translucence - opacity - absorption - reflection WHAT YOU ARE EXPECTED TO KNOW:

- Discuss and review how light travels and how it interacts with matter ✓ - Study the nature of shadows and learn what conditions are necessary to form them - Investigate the differences between point and extended light sources TODAY’S OUTCOMES: BEHAVIOR OF LIGHT