1. Energy

• Two main types of waves are mechanical and electromagnetic.

Different types of energy waves• Movement within the

Earth's crust can cause devastating seismic waves.

• Medical scientists use ultrasound and other types of waves to scan the inside of the human body.

• Civil engineers need to know how vibrations affect buildings and other

structures.

A. Mechanical Waves

• 1. These need matter to travel through.

• 2. Examples: water waves, seismic waves, and sound waves.

B. Electromagnetic Waves

1. These do NOT need matter to travel through.

2. Remember: Rowdy Martians in our unusual x-ray game.

C. How energy moves

1. Transverse waves move at a right angle (electric field moves at a right angle to the magnetic field).

• a. Light is an example.• b. The wave people create

in a ball game is another example.

• c. The movement of a guitar string is another example.

• See animated pictures @• http://www.acs.psu.edu/dr

ussell/Demos/waves/wavemotion.html

2. Longitudinal (compressional) waves

• a. These move in a back and forth motion.

• b. Sound waves are an example.

• c. Slinky waves and alternating current electricity are other examples.

3. Combinations:

• Water moves in both ways (transverse and longitudinal) forming a circular pattern.

• a. Example: when you drop a stone in a pool, the waves move outward. The water molecules actually move in a circular pattern (combination of transverse and longitudinal)/

Traveling faster than the speed of sound…is supersonic!

• Shock waves are the primary reason you hear what's called a sonic boom.

• Picture an airplane flying through the air. As the airplane moves, it pushes air molecules out of its way, continuously creating waves of compressed and uncompressed air. These air pressure waves move away from the airplane in all directions at the speed of sound (imagine ripples that form by dropping a pebble in a pond.)

Next, break the sound barrier by increasing the airplane's speed to supersonic, or faster than the speed of sound. When the airplane moves at supersonic speeds, the air pressure waves begin to pile up ahead of the airplane and compress, forming shock waves. (These are similar to a "bow wave" that piles up at the front of a boat as it moves through water.)

You can see the sonic boom

cloud as the jet breaks the

sound barrier.

• The space shuttle produced sonic booms as it left the Earth’s atmosphere. So does lightning (thunder is a sonic boom).

II.The Electromagnetic Spectrum: From the largest wave to smallest wave

A. Radio waves are the largest waves (cell phones, cable tv, radio, telescopes).

• James Clerk Maxwell predicted the existence of radio waves in the 1860’s. In 1886, German physicist, Heinrich Hertz proved the existence of radio waves.

• He used a spark gap attached to an induction coil and a separate spark gap on a receiving antenna.

• When waves created by the sparks of the coil transmitter were picked up by the receiving antenna, sparks would jump its gap as well.

Can you hear me now???

Guglielmo Marconiwas the first to send a wireless signal (using a telegraph) in 1895, but Nikola Tesla was the firstto patent it.In 1932, Karl Jansky at Bell Labs revealed that stars and other objects in space radiated radio waves.

97.5 megahertz

• Frequency is the number of cycles of a wave to pass a given point in one second.

• Measured in units called hertz.

• 97.5 as a place on the FM dial means that the radio waves are traveling 97.5 million cycles per second.

Microwaves

• B. Microwaves are used in ovens, radar, Doppler radar, and satellites.

The first microwaves didn’t cook!

• During World War II, two scientists invented the magnetron, a tube that produces microwaves.

• Installing magnetrons in Britain’s radar system, the microwaves were able to spot Nazi warplanes on their way to bomb the British Isles.

• In the 1950’s, Percy Spencer accidentally found that these microwaves had melted a candy bar in his pocket.

• Experiments showed that microwave heating could raise the internal temperature of many foods far more rapidly than a conventional oven.

• The first microwave ovens were so large (refrigerator size) that most people didn’t own one.

• It was the discovery of their reaction to metals that led to the invention of radar.

Infrared Waves

• C. Examples of infrared waves include heat, sun, tv remotes, and some satellites.

• In 1800, William Herschel conducted an experiment measuring the difference in temperature between the colors in the visible spectrum.

• He noticed an even warmer temperature measurement just beyond the red end of the visible spectrum, Herschel had discovered infrared light.

D. Optical Light

1. Roy G. Biv

2. From longest to shortest: red, orange, yellow, green, blue, indigo, violet.

• All colors are in white light.

• We use lenses to help us see: convex (in our eyes) and concave.

LIGHT!

• Isaac Newton's experiment in 1665 showed that a prism bends visible light and that each color refracts at a slightly different angle depending on the wavelength of the color.

• Many folks tried to say that something carried light. They even named this something luminiferous aether. Later scientists, including Einstein, will go on to prove this is not true.

How light moves…

• When a light wave encounters an object, it may be reflected,

absorbed,

refracted,

polarized,

diffracted,

or scattered depending on the composition of the object and the wavelength of the light.

Ultraviolet Rays

• E. UV rays come from the Sun.

• In 1801, Johann Ritter conducted an experiment to investigate the existence of energy beyond the violet end of the visible spectrum.

• Knowing that photographic paper would turn black more rapidly in blue light than in red light, he exposed the paper to light beyond violet. Sure enough, the paper turned black, proving the existence of ultraviolet light.

F. X-rays

• X-rays were named as such because the scientist who discovered them did not know what to call them.

• So, he called them

“x-rays.”

Wilhelm Roentgen x-rays his wife’s hand in 1895.

• Roentgen discovered that firing streams of x-rays through the body created images of the bones inside.

• When you get an x-ray taken, x-ray sensitive film is put on one side of your body, and x-rays are shot through you.

• Because bones are dense and absorb more x-rays than skin does, shadows of the bones are left on the x-ray film while the skin appears transparent.

Gamma rays

• G. Gamma rays are the smallest waves on the spectrum.

• They are used to kill cancer cells.

Henri Becquerel discovers gamma radiation.

• In 1896, French scientist Henri Becquerel discovered natural radioactivity.

• Many scientists of the period were working with cathode rays, and other scientists were gathering evidence on the theory that the atom could be subdivided.

• Some of the new research showed that certain types of atoms disintegrate by themselves.

• Henri Becquerel discovered this while investigating the properties of fluorescent minerals.

• One of the minerals Becquerel worked with was a uranium compound.

• Uranium ore produces naturally occurring gamma radiation. 

• The Curies will go on to work with gamma radiation further.