“Mars is the next logical step in the expansion of the human race into the stars.” -NASA If astronauts on Mars wanted to send a message back to Earth. There are two ways to do it They could enclose the message in a rocket and physically send it to Earth. Or, they could send some type of signal, maybe in the form of radio waves.

Waves A wave is a disturbance that carries energy through matter or space. It is a transfer of energy, not matter How the energy is carried defines the type of wave.

Types of Waves mechanical waves propagate through a medium. (e.g. sound, water waves, earthquakes) The medium is any material through which a wave travels (e.g. air, water, a spring, the Earth, or even people). electromagnetic waves can travel without medium, they are oscillating electric and magnetic fields (e.g. light, radio, x-rays, gamma rays).

Mechanical Waves: Three Types Mechanical waves require a physical medium. The name reflects how the particles move in the medium In a longitudinal wave, the particles in the medium move parallel to the direction of the wave. In a transverse wave, the particles in the medium move perpendicular to the direction of the wave. In a surface wave, the particles typically move in circular paths in the medium.

Transverse Longitudinal surface

For future reference… You can find all three types of mechanical waves exhibited in earthquakes.

Wave characteristics Crest and trough– The section of the wave that rises above the undisturbed position is called the crest. That section which lies below the undisturbed position is called the trough.

Wave characteristics Amplitude (A) – Maximum displacement of particle of the medium from its equilibrium point. The bigger the amplitude, the more energy the wave carries.

Wave characteristics Wavelength () – the length of one full cycle of a wave, the distance between any two adjacent corresponding locations on the wave With visible light, the wavelength determines the color

Wave characteristics Wave speed (v) – How fast the wave is moving (the disturbance itself). Speed depends on the medium. Light: 3 x 108 meters/second (300,000,000 m/s) (671,000,000 miles/hour) Sound: 343 meters/second (768 miles/hour) Fastest: solids liquids Slowest: gasses

With sound waves, frequency is called pitch Wave characteristics Frequency (f) – The number of waves passing by a point in a given period of time With sound waves, frequency is called pitch Think… what is the relationship between wavelength and frequency? what is the relationship between speed and frequency?

Speed of light verses speed of sound…

Questions?

Check for understanding

B A What is the amplitude? What is the wavelength? Which letter indicates a crest? Which letter indicates a trough?

Check for understanding If the particles of the medium move in circular paths, the wave is Surface If the particles of the medium move parallel to the wave, the wave is Longitudinal If the particles of the medium move perpendicular to the wave, the wave is Transverse

Electromagnetic Spectrum The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation. Electromagnetic radiation is self-propagating waves in a vacuum or in matter. It comprises electric and magnetic field components, which oscillate perpendicular to the direction of the wave’s travel. Check for understanding What type of wave (longitudinal, transverse, surface) are they?

Electromagnetic Spectrum

Light Waves

Wave interactions Interference When more than one wave occupies the same space the results can vary depending upon how the waves match up

Wave interactions Constructive Interference If the troughs and crests line up (even briefly), the resulting wave will have greater amplitude

Wave interactions Constructive Interference If the troughs and crests line up (even briefly), the resulting wave will have greater amplitude

Wave interactions Destructive Interference If the crest of one wave lines up with the trough of another wave, the resulting wave will have lower amplitude.

Wave interactions Destructive Interference If the crest of one wave lines up with the trough of another wave, the resulting wave will have lower amplitude.

Wave interactions http://mysite.verizon.net/vzeoacw1/wave_interference.html

Wave interactions Diffraction - refers to various phenomena which occur when a wave encounters an obstacle. It is described as the apparent bending of waves around small obstacles and the spreading out of waves past small openings.

Wave interactions Diffraction

Wave interactions Diffraction

Wave interactions Diffraction

Wave interactions Refraction - is the change in direction of a wave due to a change in its speed. This is most commonly observed when a wave passes from one medium to another at an angle.

Wave interactions Refraction

Wave interactions Refraction

Questions?

Check for understanding Which type of wave is this?

Check for understanding Which type of wave is this?

Check for understanding What is it called when two waves occupy the same space at the same time? interference If the resulting wave is smaller, that interference is… destructive If the resulting wave is bigger, that interference is… constructive

Check for understanding The bending of waves around an object is… diffraction The bending of waves as they pass from one medium through another is… refraction

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