5/24/10

Post date: May 24, 2010 6:9:2 PM

Bell Ringer: What factors influence how fast a wave travels?

    • Finish wave speed lab (due tomorrow)

    • Notes - waves

      • wave speed depends on

        • the medium

          • temperature of the medium (how fast the molecules move) - hotter temperature --> faster waves

          • The distance between particles (solids have molecules that are closer together than liquids or gases, so waves (like sound) travel fastest through solids.

        • The type of wave

          • e.g. light waves travel faster through air than sound waves

      • Light has a finite speed

        • light doesn't move instantly, it takes some time for light (radio, x-ray, all EM waves) to reach their destination

        • Light travels a distance of one light year per year - so light from a star 20 light years away has been traveling for 20 years

        • When we look at stars, we see what the star looked like when the light left that star, some time in the past. Some of the stars we see in our sky may already be dead, but are very far from Earth so we can't see it's absence yet.

        • Light from the sun takes 8 minutes to get to Earth - the sun may have disappeared 6 minutes ago, but we won't know it for another 2 minutes!

      • The Doppler Effect

        • when the source of waves is moving, and observer will encounter waves of a different frequency than what the source emits

        • When a car come toward us, we hear a higher pitch from its engine. When it moves away, we hear a lower pitch.

  • Page 523: 1-9 due tomorrow