1/5/09

Post date: Jan 04, 2009 7:8:53 PM

Bell Activity: What happens to radio and TV transmissions that are sent upward, into space?

• • Hand out sound test

    • due Wednesday

    • Late tests will lose 15% per day late

  • View intro to Contact.

    • What happens to the transmissions as we get farther from the Earth? They get older.

    • Why do they get older? The older transmissions have had more time to travel, and have gotten farther.

• Transmitting your birth

  • • Assume you just found out that your birth was filmed and broadcast into space.

    • Using 3.00 x 10^8 m/s as the speed of the transmission, how far from Earth (in meters) is that transmission now?

    • You will use the first velocity equation that we used in this class for this problem

    • Title this page "Light speed homework"

• • Light is a wave, so we'll look at wave behaviors for light

    • reflection

    • refraction

    • diffraction

    • interference

    • frequency, wavelength, wave speed

    • wave speed depends on medium light is traveling through

      • in a vacuum (empty space), speed of light is about 3.00 x 10^8 m/s, or 186,000 miles per second

  • The speed of light in a vacuum or in air is about 300,000,000 m/s

    • This value is referred to as "c".

    • We can rewrite the wave equation as c = frequency times wavelength for light in a vacuum

    • At this speed, light can circle the Earth about 8 times in a second.

    • It takes light just over 8 minutes to reach us from the sun, because that is such a huge distance.

    • Because we deal with such large numbers, it's important to understand use the metric prefixes. These can be found on page 711 of your book.

      • • In order to communicate effectively in this subject, students should memorize the meanings and values associated with the prefixes nano, micro, milli, centi, kilo, mega, and giga.

  • The electromagnetic spectrum

• • • Radio waves, microwaves, infrared, ultraviolet, x rays, and gamma rays are all the same type of wave as visible light.

    • Our eyes are only sensitive to the part labeled visible light

      • from about 400 nm to 700 nm (nm = nano meter = 1 billionth of a meter)

      • Other animals are sensitive to other parts of the spectrum

        • Mosquitoes see in infrared

        • Bees see in ultraviolet

• • We still use the wave equation with EM (electromagnetic) waves such as light

    • Unless we are told otherwise, assume the speed of these waves is 3.00 x 10^8 m/s

    • Due page 332: 1-5 for practice with this

      • do this on the "Light speed homework" page you started earlier