8. When light (or other electromagnetic radiation) travels across a given region, what is it that oscillates? What is it that is transported? 9. In space sailing, which is a proposed alternative for transport to the planets, a spacecraft carries a very large sail. Sunlight striking the sail exerts a force, accelerating the spacecraft. Should the sail be absorptive or reective to be most effective? 10. How can the average value of an alternating current be zero, yet the square root of the average squared value not be zero? 11. Suppose a creature from another planet had eyes that were sensitive to infrared radiation. Describe what it would see if it looked around the room that you are now in. That is, what would be bright and what would be dim? 12. Why should an infrared photograph of a person look different from a photograph taken using visible light?