Waves

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# Waves - PowerPoint PPT Presentation

Waves. Radio waves, x-ray, light, sound, seismic waves (p waves, s waves), waves at the beach!. Definition of wave. 1. A wave is a disturbance that travels through matter (air, water, rock) OR space (no matter) 2. Waves carry or transmit energy. . 2 Kinds of Waves. Mechanical Waves

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### Waves

Radio waves, x-ray, light, sound, seismic waves (p waves, s waves), waves at the beach!

Definition of wave
• 1. A wave is a disturbance that travels through matter (air, water, rock) OR space (no matter)
• 2. Waves carry or transmit energy.
2 Kinds of Waves
• Mechanical Waves
• A mechanical wave travels through a medium. Air, water, earth, are different mediums
• Electromagnetic Waves
• Electromagnetic waves are produced by the motion of electrically charged particles
Mechanical waves

1. Transverse wave: particles move up and down while the wave moves left or right; particles move perpendicular to the path of the wave.

2. Longitudinal waves (slinky, sound waves) particles move back and forth, or parallel to the path of the wave.

3. Surface waves (beach ball example) combination of transverse and longitudinal.

Electromagnetic waves

1. Transverse wave: particles move up and down while the wave moves left or right.

Types of Waves
Websites for wave action
• http://paws.kettering.edu/~drussell/Demos/waves/wavemotion.html
Parts of a transverse Wave
• Crest is the high point of the wave
• Trough is the low point of the wave
• Amplitude: Height of the wave from the resting point to the crest (+) or height of the wave from the resting point to the trough (-)
• Wavelength (symbol λ lambda) The distance from crest to crest or trough to trough.
Frequency
• The number of wavelengths in one second Units are 1 = hertz

sec

• If two waves have the same wavelength but are traveling at different speeds, the wave that is traveling faster will have a higher frequency.
Period
• Period: the time it takes for one full cycle (wavelength) of the wave to pass by a given point.
• Units are a time like seconds
Period: the time it takes for one full cycle (wavelength) of the wave to pass by a given point.

Frequency: the number of wavelengths per second

Wavelength: the distance from peak to peak or trough to trough.

Speed= wavelength period

Frequency= speed

wavelength

Formulas
Light is a type of electromagnetic radiation.It can be described in two ways.
• Wave model
• transverse waves
• Particle model of light
• Photon: a “particle” of light that has no mass.
• A stream of photons make up a “beam of light”
• Photons are produced when electrons drop from a high energy level to a low energy level.
The Electromagnetic Spectrum
• Definition: The full range of wavelengths of electromagnetic radiation
• Visible Light is only one tiny part of the electromagnetic spectrum.
• A nanometer is one billionth of a meter or 10-9 meters
Examples of the Electromagnetic Spectrum Diagrams

http://www.dnr.sc.gov/ael/personals/pjpb/lecture/spectrum.gif

http://www.lcse.umn.edu/specs/labs/images/spectrum.gif

http://cassini-huygens.jpl.nasa.gov/mission/images/EM-spectrum.jpg

http://www.antonine-education.co.uk/physics_gcse/Unit_1/Topic_5/em_spectrum.jpg

Visible Light
• VISIBLE LIGHT: Each different color has its own wavelength
• ROY G BIV (red, orange, yellow, green, blue, indigo, violet)
• Red light has the longest wavelength
• Blues are shorter and violet has the shortest wavelength
Scientific Notation
• A method for expressing a large number
• Numbers are multiplied by powers of 10
• Example #1
• The speed of light is 300,000,000 m/sec
• 300,000,000 m/sec = 3 x 108 m/s
• Example #2
• 4,500,000,000,000m = 4.5 x 1012m
Example problem #1
• To use a shortcut for scientific notation, move the decimal point and count the number of places it is moved. To change 18,000 to scientific notation,
• move the decimal point four places to the left until you have 1.8 and the number of places that the decimal is moved is the correct power of 10.

18,000 L = 1.8 x 104 L

Example Problem #2
• When a quantity smaller than 1 is converted to scientific notation, the decimal moves to the right and the power of 10 is negative. To express 0.0000021 M in scientific notation. . .
• move the decimal point to the right 6 places.

0.0000021 m = 2.1 x 10-6m

• Longest wavelength in the electromagnetic spectrum
• 1x 10-1 and longermeters wavelength
• Used for things like radar systems
• Frequency: 3x109 hertz or less
• Energy: 2 x 10-24 Joules or less

Microwaves
• Wavelength: 1x 10-3 m to 1x 10-1 m
• Used in cooking (microwaves) and communication (cell phones)
• Frequency: 3x109 to 3 x 1011 hertz
• Energy: less then 2 x 10-24 Joules

Infrared light (IR)
• Wavelength: 7x10-7 to 1x10-3 m
• Use:
• Infrared light from the sun warms you.
• Frequency: 3x1011 to 4 x 1014 hertz
• Energy: less then 2 x 10-22 to 3x10-19Joules

Visible Light(also called optical)
• Wavelength:

4 x 10-7m to 7 x 10-7 m

• The colors that we can see
• Frequency:

4x1014 to 7.5 x 1014 hertz

• Energy:

10-19 to 5x10-19Joules

/data/media/13/rainbow-over-the-muldrow-glacier_1127.jpg

Ultraviolet Light
• Wavelength:

1 x 10-8 to 4 x 10-7 m

• Use: Some insects can see ultraviolet, causes a sunburn Frequency:

7.5x1014 to 3 x 1016 hertz

• Energy:

5 x 10-19 to 2x10-17Joules

http://www.crackedanimations.com/portfolio/drawings/sunburn.jpg

X rays
• Wavelength: 1 x 10-11 - 1 x 10-8m
• Used for x ray imaging
• Frequency: 3x1016 to 3 x 1019 hertz
• Energy: 2 x 10-17 to 2x10-14Joules

Gamma Rays
• Shortest Wavelength in the Electromagnetic spectrum
• Wavelength 1 x 10-11 m and smaller
• Uses: gamma rays are used in “radiation therapy” to kill cancer cells. Emitted from nuclear reactions damages living cells.
• Frequency: 3x1019 or greater hertz
• Energy: 2 x 10-14 Joules or greater

Spectra from a fluorescent light bulb

Different kinds of elements each give off a different spectra.

United streaming: Exploring Space: the Universe: “spectroscope”

A spectroscope is a tool that will separate visible light into the bands or spectrum of different colors.
Spectra of Stars
• By knowing the spectra given off by stars we can tell:
• Elements they are made of
• Temperature
• Pressure
• Magnetic field
• Can tell If distance between the Earth and the star is increasing or decreasing
3 TYPES OF SPECTRA

http://csep10.phys.utk.edu/astr162/lect/light/spectra.gif

Three main types of spectraType one: continuous spectrum
• 1. Continuous unbroken band of colors all wavelength’s or colors of the electromagnetic spectrum.
• Made from objects that are
• hot solids (like a hot wire in an electric light)
• hot liquids (like molten iron)
• or compressed gasses deep in a star.

http://www.astronomynotes.com/light/rainbow.jpg

Type Two: Bright line or emission spectrum
• 2. Bright line or emission spectrum are unevenly spaced series of lines of different colors and brightness.
• Made from objects containing elements that are in the form of glowing thin gas or vapor.
• Each element has its own unique spectra.
Example of different bright line spectra from: http://members.misty.com/don/spectra.gif
Type Three: Dark-line spectra or absorption spectrum
• 3. Dark Line or absorption spectrum dark lines are where light is absorbed. Shows composition of the stars outer layer or the planet's atmosphere.
• Interiors of star’s or planets emit continuous spectrum but some of the radiation is absorbed by that objects atmosphere. This forms the dark lines in a spectrum.
• They are in the same place as the bright lines for the same element in a bright line spectra.
• http://hea-www.harvard.edu/~efortin/thesis/html/Spectroscopy.shtml

### Doppler effect

http://www.grc.nasa.gov/WWW/K-12/airplane/sndwave.html

Police Car Siren
• As the siren approaches you, the waves of sound are squeezed together, and you hear them as being higher-pitched.
• After the car passes by, sound waves from the receding siren are stretched apart. You hear these stretched waves as being lower-pitched.

Wavelengths from the perspective of the ear not the car.

Stars: cosmic police cars
• A star zooming toward you has its light waves squeezed together. You see these light waves as having a higher frequency than normal. The light from an approaching star is shifted toward blue end of the spectrum, or blue-shifted.
• A star zooming away from us has light waves stretched out and lower frequency then normal, the light is shifted toward red, red-shifted.
Doppler Effect

http://www.cnrt.scsu.edu/%7Edms/cosmology/DopplerEffect/doppler2.gif

The arrows show how the direction a star is moving relative to Earth affects the way we see light.
• If shifted toward blue end of spectrum the distance is decreasing.
• If shifted toward red end the distance is increasing.
• Image: Holt Physical Science p 710, 2008
As the distance between the Earth and a star increase the spectra is shifted toward the red end.

http://www.astro.ucla.edu/~wright/redshift.gif