Waves

Homework

Objectives Become familiar with the electromagnetic spectrum

Wave Theory: Review Make waves, check properties

Wave Properties The property of a wave isnt just math to play with, it affects what the wave is and does. Who remembers: Does anybody know what makes a sound appear to be higher or lower in pitch? What makes it appear louder or softer?

Wave Properties The frequency of a sound wave determines whether its a high sound or a low sound. The amplitude of a sound wave determines whether its loud or quiet. Wave properties will be especially important right now to understand about electromagnetic (EM) waves…

Electromagnetic Waves Electromagnetic waves are transverse waves. But although they may travel through a medium (or they may not), in EM waves, its not the medium thats oscillating (moving or vibrating). Its an electrical or magnetic field that is.

Electromagnetic waves Wavelength determines what kind of EM wave it is. (You could also say that frequency does, since they are directly correlated.) The range of EM wave wavelengths/frequencies is called the electromagnetic spectrum. Amplitude determines intensity/brightness.

Electromagnetic spectrum (1st half): Bill Nye Waves:

EM Spectrum

Electromagnetic waves EM waves are the only tool that we have for studying the universe, but they are a powerful tool that can tell us a lot. Two key pieces of info we can get from a star or other objects EM waves are what its made of, and what direction its moving in. Take a moment and talk with your partner, lay out everything youve ever heard about Big Bang Theory.

Big Bang Theory The Big Bang Theory is the model of the universe best supported by all our current evidence. The universe expanded from a hot primordial condition, and is still expanding today. Learn about two cool but simple pieces of key evidence from which we figured it out.

Cosmic Background Radiation We watched a movie several weeks ago that introduced you to this. Now that you know a bit more about waves, the movie should make more sense. Rewatch a clip of it, and then youll be asked to write a paragraph explaining cosmic microwave background radiation that uses the vocab words I assign.

Big Bang Theory To understand this piece of evidence, a demonstration will help. Be thinking about how to explain what you observe using your knowledge of waves.

Doppler Effect The Doppler Effect = the change in frequency & wavelength of a wave for an observer who is moving relative to the waves source. ulEYSgk ulEYSgk

Doppler Effect It applies to EM waves (including light) as well as to sound and other mechanical waves. If an object is giving off light, and the two of you arent perfectly stationary in relation to each other, the wavelengths of the light waves will be longer or shorter depending on whos moving where. If something is moving towards you, will its color be more blue or more red?

Doppler Effect and Redshift Scientists have known for more than 150 years that the light from most stars, nebulas, galaxies, etc. is redshifted, or is more red than it should be. This means that most parts of the universe are moving away from us. When these movements are mapped, its clear that this means the universe is expanding.

Doppler Effect Draw two diagrams, and write an explanation below each, of how Doppler Shift works for sound, and for light.