1. Under what conditions is the material invisible? Explain.

2. Why can you see ice cubes in a glass of water if both the ice and water are made of the same substance? Explain.

3. H.G. Wells, author of the science-fiction classics "The Time Machine" and "The War of the Worlds", also wrote the intriguing novel entitled "The Invisible Man". What physical characteristics would a person need to be invisible? Explain