Discovery Science Waves Sp2011

Chapters 17 & 18

Key Terms Wave- a disturbance that transmits energy

through matter or space Medium- the matter through which a wave

travels Mechanical wave- a wave that requires a

medium through which to travel Electromagnetic wave- caused by a

disturbance in electric and magnetic fields. Does not require a medium

Waves transfer energy Ability to do work waves carry energy bigger the wave, the

more energy it carries Energy may spread

out as the wave travels

Wave spread out in spheres that get bigger as the wave moves from the center

Transverse and longitudinal waves

Transverse waves include all electromagnetic [radio, radar, i.r., visible, u.v., X-rays]

have perpendicular motion http://www.surendranath.org/Applets/Waves/Lwave01/Lwave01Applet.html

longitudinal waves are sound waves. Have parallel motion http://www.cbu.edu/~jvarrian/applets/waves1/lontra_g.htm

Wave properties

A wave is a pattern in the value of some quantity which is changing at every point of space.

Wave Properties Crest- Highest point of a transverse wave Trough- the lowest point of a transverse wave Amplitude- greatest distance that particles in a

medium move from their normal position when a wave passes

The amplitude is the height of the wave. The wavelength is the distance from one wave

top, or crest, to the next.

amplitude

amplitude

wavelength

Wave properties 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.

Period- Time required for one full wavelength to pass a certain point.

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

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

Frequency- Period Equation

Wave speed The speed at which a wave passes through a

medium Wave speed, wavelength, and frequency are related

by the equation: v = f λ

The speed of a wave depends upon the material it is traveling through.

Electromagnetic Wave

Click here for simulation Sketch the two parts

Electromagnetic Spectrum

f f f f f f f f f

R O Y G B I V

http://www.colorado.edu/physics/2000/waves_particles/index.htmlhttp://www.colorado.edu/physics/2000/waves_particles/index.htmlhttp://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.htmlhttp://www.walter-fendt.de/ph11e/emwave.htm

Doppler effect

Whenever relative motion exists between a source of sound and a listener, the frequency of the sound is as heard by the listener is different compared to the frequency when there is no relative motion

The Doppler Effect Heard an ambulance go by recently? Remember how the siren's pitch

changed as the vehicle raced towards, then away from you? First the pitch became higher, then lower. Originally discovered by the Austrian mathematician and physicist, Christian Doppler (1803-53), this change in pitch results from a shift in the frequency of the sound waves

As the ambulance approaches, the sound waves from its siren are compressed towards the observer. The intervals between waves diminish,

which translates into an increase in frequency or pitch (fffff)

As the ambulance recedes, the sound waves are stretched relative to the observer, causing the siren's pitch to decrease. By the change in pitch of the siren, you can determine if the ambulance is coming nearer or speeding away. If you could measure the rate of change of pitch, you could also estimate the ambulance's speed.

Doppler Effect By analogy, the electromagnetic radiation emitted by a moving object also exhibits the

Doppler effect. The radiation emitted by an object moving toward an observer is squeezed; its frequency

appears to increase and is therefore said to be blue-shifted. In contrast, the radiation emitted by an object moving away is stretched or red-shifted. As in the ambulance analogy, blue-shifts and red-shifts exhibited by stars, galaxies and gas

clouds also indicate their motions with respect to the observer.

f f

Doppler Effect Blue shifted = higher frequency = higher pitch. Red shifted = lower frequency = lower pitch. Electromagnetic Spectrum

f f f f f f f f f

The Doppler Effect In Astronomy

Click here for video clip In astronomy, the Doppler effect was originally studied in the visible part

of the electromagnetic spectrum. Today, the Doppler shift, as it is also known, applies to electromagnetic

waves in all portions of the spectrum. Also, because of the inverse relationship between frequency and wavelength, we can describe the Doppler shift in terms of wavelength.

Radiation is red-shifted when its wavelength increases, and is blue-shifted when its wavelength decreases.

A red-shift occurs when the source and observer are moving away from each other.

A blue-shift occurs when the source and observer are moving towards each other.

Here is what the spectrum of a star that is moving toward us might look like (Blue-shift)

Here is what the spectrum of a star that is moving away from

us might look like (red-shifted)

Gravitational Red-shift

According to General Relativity, the wavelength of light (or any other form of electromagnetic radiation) passing through a gravitational field will be shifted towards redder regions of the spectrum.

To understand this gravitational red-shift, think of a baseball hit high into the air, slowing as it climbs.

Einstein's theory says that as a photon fights its way out of a gravitational field, it loses energy and its color reddens.

Gravitational red-shifts have been observed in diverse settings.

Wave interactions Reflection- the bouncing back of a wave as it

meets a surface or boundary Diffraction- the bending of a wave as it

passes an edge or an opening. Animation 2 Refraction- the bending of waves as they

pass from one medium to another. What’s critical angle?

Interference- the combination of two or more waves that exists in the same place at the same time.

http://www.lon-capa.org/~mmp/kap13/cd372.htm

Why is the sky blue and sunsets red?

Angle of Incidence    The angle at which a ray of light approaches a surface, reflective or not, is called the angle of incidence. It is measured from an imaginary line perpendicular to the plane of the surface in question to the incoming ray of light.

Angle of ReflectionOnce the light has reflected from a reflectivesurface, the angle at which the light departs fromthe surface is called the angle of reflection.

This angle is also measured from a perpendicularto the reflecting surface to the departing ray oflight.

When light reflects from a surface, the angleof reflection is always equal to the angle ofincidence.

Standing Waves Standing waves are non-traveling vibrations of certain

wavelength and frequency which occur on a medium of certain size

The size of the medium controls the wavelengths of the standing waves

the way that the medium is held at its ends, either fixed or open, controls the wavelengths of the standing waves.

http://id.mind.net/~zona/mstm/physics/waves/standingWaves/standingWaves1/StandingWaves1.html

Node and antinodes Node- medium does not move and have no vibration Antinode- form where the crests of the original waves

line up with crests of the reflected waves so that complete constructive interference occurs

Point of maximum vibration

http://www.physics.smu.edu/~olness/www/05fall1320/applet/pipe-waves.html