Let’s review…..

• Waves

Electromagnetic Waves

Mechanical Waves(sometimes called elastic)

Do not need a medium (material) to travel through

Need a medium (material) to travel through

Waves produced due to changes in electric and magnetic fields

Waves are produced due to the vibration of the medium

Have fast speed Have slow speed

An example of a transverse wave:

In the above diagram the white line represents the position of the medium when no wave is present.

The yellow line represents the position of the medium as a wave travels through it. We simply say that the yellow line is the wave.

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. These sections are labeled in the following diagram:

Amplitude

http://id.mind.net/~zona/mstm/physics/waves/introduction/introductionWaves.html

Amplitude is the measurement of the energy carried by any wave. It is the farthest distance that the particles move from the wave’s undisturbed position, or when the wave is flat, due to the energy passing through it.

Wavelength

The wavelength of a wave is the distance between any two adjacent corresponding locations on the wave train. This distance is usually measured in one of three ways: crest to next crest, trough to next trough, or from the start of a wave cycle to the next starting point

Frequency• Frequency refers to how many waves are made

per time interval. This is usually described as how many waves are made per second, or as cycles per second.

• Usually, we use the unit Hertz to state frequency. A frequency of 10 cps is noted as a frequency of 10 Hertz. So, one cycle per second is one Hertz, as in: 1 cps = 1 HertzThe unit Hertz is abbreviated this way:1 Hertz = 1 Hz

http://id.mind.net/~zona/mstm/physics/waves/partsOfAWave/waveParts.htm

Interactions of waves

• We will discuss– Reflection– Refraction– Diffraction– Absorption

Reflection• When an object

or a wave hits a surface through which it cannot pass, it bounces back. This interaction with a surface is called reflection.

• All waves, not just light waves, are reflected whenever they hit a surface they cannot pass through.

• How can you tell when sound waves are reflected back from a surface?

http://id.mind.net/~zona/mstm/physics/light/rayOptics/reflection/reflection1.html

Refraction

• When a wave enters a new medium at an angle, one side of the wave changes speed before the other side, causing the wave to bend. The bending of waves due to a change in speed is called refraction.

simple refraction, one that happens at a flat boundary

As the speed of the wave is reduced in the slower medium, the wavelength is shortenedproportionately.

Remember……

• Refraction occurs only when one side of the wave enters the new medium and changes speed before the other side. The wave bends as the two sides of the wave travel at different speeds.

• What characteristics must a new medium have to cause refraction?

Diffraction

• When a wave moves around a barrier or through an opening in a barrier, it bends and spreads out. These wave interactions are called diffraction.

Diffraction of water waves

• diffraction occurs when waves pass around the edge of, or through a hole in, a barrier.

• What happens to waves when they go around a barrier?

• When they go through a hole in a barrier?

Absorption• Absorption is the process by which energy is retained by a

substance.

• Examples: • In meteorology global and local temperatures partly depend

on the absorption of radiation by atmospheric gases (such as in the greenhouse effect) and the ground.

• In medicine, X-rays are absorbed to different extents by different tissues (bone in particular), which is the basis for X-ray imaging.

• In optics, sunglasses, colored filters, dyes, and other such materials are designed based on which visible wavelengths they absorb and how much.

• In biology, photosynthetic organisms require that light of the appropriate wavelengths be absorbed within the active area of chloroplasts, so that the light energy can be converted into chemical energy within sugars and other molecules

Wave Interference

• Interference is the interaction between waves that meet. There are two types of interference: constructive and destructive.

Constructive Interference The interference that occurs when waves combine to make a wave with a larger amplitude is called constructive interference.

• Destructive Interference The interference that occurs when two waves combine to make a wave with a smaller amplitude is called destructive interference. You can think of destructive interference as waves subtracting their energies.

Standing waves…

Constructive

Destructive

Antinode

Node

A standing wave, also known as a stationary wave, is a wave that remains in a constant position. This phenomenon can occur because the medium is moving in the opposite direction to the wave, or it can arise in a stationary medium as a result of interference between two waves traveling in opposite directions.

Resonance

• Resonance is an increase in the amplitude of a vibration that occurs when external vibrations match an object’s natural frequency.

Standing waves in resonators are one cause of resonance.

Seismic Waves

• The waves produced by earthquakes are called seismic waves. (The word seismic comes from the Greek word seismos, which means “earthquake.”)

• P Waves Some seismic waves are longitudinal waves.

• Longitudinal seismic waves are known as P waves, or primary waves.

• They are called primary waves because they move faster than other seismic waves and so arrive at distant points before other seismic waves.

• P waves are made up of compressions and rarefactions of rock inside Earth. These waves compress and expand the ground like a spring toy as they move through it.

• S Waves Other seismic waves are transverse waves with crests and troughs.

• Transverse seismic waves are known as S waves, or secondary waves.

• S waves shake the ground up and down and side to side as they move through it.

Surface Waves:• When P waves and S waves reach Earth’s

surface, they can create surface waves.

• A surface wave is a combination of a longitudinal wave and a transverse wave that travels along the surface of a medium.

• Surface waves produced by earthquakes move more slowly than P waves and S waves.

• Earthquakes that occur underwater, like the one off the coast of Sumatra, Indonesia, in 2004, can produce huge surface waves on the ocean called tsunamis.

• Tsunamis come in all sizes, from 2 centimeters to 30 meters tall.

• They can travel thousands of kilometers across the ocean.