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Lesson Three “How Does Light Travel?” and Lesson 4 “Blocking the Light” Review Sheet

Lesson 3: How does light travel?

Key Terms: Light Year

1.  Does light travel through air and water?

-  Yes, light can travel through air and water.

2.  What do you need to do to detect light?

-  Place a form of matter in front of the light source that intercepts the path of light and reflects light back to our eyes.

3.  What is a light year? What does a light year measure?

-  A light year is the distance light travels in one year. It measures distance, not time.

4.  Consider why you can never see things in outer space exactly at that moment? What about on Earth? (Use the diagram below to answer the question)

-  It takes time for light to travel back to our eyes, even though light travels very fast. The time it takes for light to travel to our eyes depends on how far the light source is from us. It still takes time for light to reach our eyes from objects here on Earth, but it is a much shorter time than distant objects, like the Sun, Mars, and stars.

Lesson 4: Blocking the Light

Key Terms: Transparent, Translucent, and Opaque, Eclipses

1.  What is a translucent object? Give an example.

-  An object that allows some light to pass through. Examples: Frosted glass, wax paper, fog (clouds)

2.  What is a transparent object? Give an example.

-  An object that you can easily see through, because it allows all light to pass through. Examples: Clear glass, water, clear plastic, air

3.  What is an opaque object? Give an example?

-  An object that allows no light to pass through. Examples: wood, concrete, book, animals (hippo), tin foil, food

4.  How are shadows produced? What happens to the size of a shadow when the object is closer/further away from the light source?

-  Shadows are produced when an object blocks light. When an object is closer to a light source, the shadow size increases. When the object is further away, the shadow size decreases.

5.  What is a point light source? What types of shadows does it produce? What is a diffuse light source? What type of shadows does it produce?

-  A point light source is a horizontal light source and it produces only an umbra (dark, sharp shadow). A diffuse light source is a vertical light source and it produces an umbra and a penumbra (light, fuzzy shadow).

6.  What is produced when shadows are formed on an astronomical scale? What are they called?

-  Eclipses are produced when shadows form on an astronomical scale; they are called solar and lunar eclipses.