General Wave Properties S.K DHAR

What is a wave? A wave is a transfer of energy from one point to another via a traveling disturbance A wave is characterized by its wavelength, frequency, and amplitude

Transverse Waves that travel perpendicular to the direction of motion Examples: Light, -p waves for earthquakes, Ocean waves

Longitudinal Waves that travel parallel to the direction of motion Made up of compressions and rarefactions in the medium that they are traveling incompressions Examples: sound waves and s waves for earthquakes

Do You See The Difference Between Transverse And Longitudinal Waves?Transverse And Longitudinal Waves

Wavelength (λ) Distance from successive crest to crest or trough to trough Measured in meters

Frequency Number of crests passing by per second Measured in Hertz (Hz) defined to be one cycle per sec Equal to the inverse of the amount of time it takes one wavelength to pass by

Amplitude Maximum displacement of the wave The amplitude will have different units depending on the type of wave In a sketch of the wave, it is the distance from the middle of the wave to the peak

Wave Speed Where, v is the speed of the wave (m/s) λ is the wavelength in meters (m) f is the frequency in Hertz (cycle/s) Traveling Waves move through space at a certain speed

Matter / Quantum Waves Electrons and other tiny particles show wave-like properties A particle moving close to the speed of light (c) can diffract or bend around the edges of objects Also, particles do exhibit interference which is a wavelike property Any moving matter has wave characteristics in theory BUT the wavelength of any life-size particle, like a golf ball, is so small that it is negligible

If we can sometimes consider an electron to be a wave, what is its wavelength?

Its wavelength depends on its momentum or where p is momentum in kg*m/s, h is Planck’s constant = 6.63 x J, and λ is the wavelength in meters

What is Planck’s constant? Planck’s Constant is the size where quantum mechanics becomes necessary Since "Planck's Constant" (‘h’= 6.63 x Js) is such a tiny number, quantum mechanics is needed only at very small scales An electron also has spin that is quantized in units of h.quantized These units (Joule-sec) are units of angular momentumangular momentum

Electromagnetic Waves Waves of energy emitted from any accelerating charges Any object that is above absolute zero emits electromagnetic waves The entire range of possibilities is called the “Electromagnetic Spectrum.” Still confused? Then click What are electromagnetic waves?

Electromagnetic Waves Wavelength is : Where, c is the speed of light (3 x 10 8 m/s in a vacuum) λ is the wavelength in meters f is the frequency in Hertz And h is Planck’s constant (there it is again- do you remember its value?) E is the energy of a photon in Joules

What is this “photon” term you’re throwing in there? A photon is a bundle (quantum) of light A photon has energy equal to Recall that h is Plank’s constant ν is the frequency of the radiation (wave)

What does a photon do? Both magnetic and electric forces involve the exchange of photons The photon has zero rest mass, but has momentum, can be deflected gravity, and can exert a force

The Electromagnetic Spectrum Think you know all about the electromagnetic spectrum? Well take a tour of the Electromagnetic Spectrum to find out more cool information. Then, if you’re brave enough, take the electromagnetic quiz. Remember to run the applet at the top of the page.

TYPES OF ELECTROMAGNETIC WAVES GAMMA RAYS Emitted from the nuclei of atoms during radioactive decay or during high- speed collisions with particles. Ionizing Used in cancer treatment and for sterilization Sources: Cobalt 60, the inner core of the sun

X-RAYS Emitted when an electron moves from certain excited states back down to its ground state, or when an electron that is moving very quickly is suddenly stopped Two groups - long wavelength (soft x-rays) and shorter wavelength (hard x- rays) Used for radiography (x-ray photography) and to look at materials in industry for defects Sources: emitted by heavy atoms after bombardment by an electron

ULTRAVIOLET Above the color violet Three groups - UV A, UV B, and UV C. “A” type: longest wavelength; least harmful UV B and UV C are absorbed by DNA in cells Used by the body to produce vitamin D, to kill bacteria on objects, and for sun tanning Sources: Ultra hot objects 5000°C or more

VISIBLE LIGHT White light: combination of all the colors Rainbow: example of white light that has been separated into a continuous spectrum of colors The names of colors are assigned in order of their wavelengths Used for communications (fiber optics) Sources: very hot objects ColorWavelength intervalFrequency interval red~ 625 to 740 nm~ 480 to 405 THz orange~ 590 to 625 nm~ 510 to 480 THz yellow~ 565 to 590 nm~ 530 to 510 THz green~ 520 to 565 nm~ 580 to 530 THz cyan~ 500 to 520 nm~ 600 to 580 THz blue~ 430 to 500 nm~ 700 to 600 THz violet~ 380 to 430 nm~ 790 to 700 THz

INFRARED Thought of as heat but is not always Far infrared energy is heat energy. All objects that have warmth radiate infrared waves Easily absorbed and re- radiated. Used in remote controls, surveillance, therapy of muscles Sources: Humans, the sun

MICROWAVES 1 mm-1 dm in length Absorbed by water molecules – how microwave ovens heat food Used in telecommunications and power transmission Sources: electric circuits, many stars, microwave ovens

RADIO WAVES 10 cm- 100,000+m in length Only cosmic waves the reach the surface of the Earth Cause of noise Divided into smaller frequency dependent groups called bands Used for communications Sources: transmitters and sparks from motors

Polarization Electric and magnetic fields which make up wave have preferred directionElectric and magnetic fields Can be horizontal, vertical, circular, or elliptical Most radio emission is unpolarized To learn more click herehere

Polarization x y Electric Field Magnetic Field Electromagnetic Wave x y z E Horizontal Polarization Electric Field Magnetic Field Electromagnetic Wave x y z E Vertical Polarization

Why Do We Care About Radio Waves? Gadgets- cell phones, microwaves, remote controls, garage door openers Science- radio astronomy, atmospheric research