Waves, Electromagnetism, & Electrons

Waves, Electromagnetism,

& Electrons

By : Ma. Silverman

A Quick Lesson on Waves

By: M. Silverman

Wave Parts

Crest – the highest point on the wave.Trough – the lowest point on the wave.

Amplitude – the wave height, equivalent to brightness in light waves.

Amplitude is the distance size of compressions in sound waves and causes changes in volume or loudness of sound.

The wavelength, lambda, λ, is the distance from crest to crest or trough to trough.

Longitudinal Waves In a longitudinal wave the particle displacement is parallel to the direction of wave propagation. The animation below shows a one-dimensional longitudinal plane wave propagating down a tube. The particles do not move down the tube with the wave; they simply oscillate back and forth about their individual equilibrium positions. Pick a single particle and watch its motion. The wave is seen as the motion of the compressed region (i.e., it is a pressure wave), which moves from left to right.Sound waves are an example of longitudinal waves.

Animation courtesy of Dr. Dan Russell, Kettering University

Transverse Waves In a transverse wave the particle displacement is perpendicular to the direction of wave propagation. The animation below shows a one-dimensional transverse plane wave propagating from left to right. The particles do not move along with the wave; they simply oscillate up and down about their individual equilibrium positions as the wave passes by. Pick a single particle and watch its motion.

Animation courtesy of Dr. Dan Russell, Kettering University

Water Waves Water waves are an example of waves that involve a combination of both longitudinal and transverse motions. As a wave travels through the waver, the particles travel in clockwise circles. The radius of the circles decreases as the depth into the water increases. The movie below shows a water wave traveling from left to right in a region where the depth of the water is greater than the wavelength of the waves. I have identified two particles in blue to show that each particle indeed travels in a clockwise circle as the wave passes.

Animation courtesy of Dr. Dan Russell, Kettering University

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.

If ten waves are made per second, then the frequency is said to be ten cycles per second, written as 10 cps.

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 Hertz

The unit Hertz is abbreviated this way:1 Hertz = 1 Hz

http://id.mind.net/~zona/mstm/physics/waves/wave3d1/wave3d1.htm

Low frequency

High frequency

Note the relationship between frequency wavelength

Frequency, Wavelength and Period

The following equations are useful: •c = λν, where c = speed of light = 2.998 x 108 m/s , lambda, λ = wavelength, and nu, ν = frequency.•E = hν, where E = energy, h = Planck’s constant = 6.0626 x 10-34 J . s, and ν = frequency.•E = mc2 ,where E = energy, m = mass, and c = speed of light = 2.998 x 108 m/s. Sample problem:  How much energy is in single photon of Gamma ray, λ = 0.1 A (1 A = 1.0 x 10-10 m)?

How much energy in 5 x 1030 photons?                                                                   

• Snakes “see” infrared• Bees see ultraviolet

Frequency gives sound its pitch.

High frequency gives high pitch. Low frequency gives low pitch.

Click on speaker

High or low frequency?

Wave Behavior

Refraction

DiffractionDiffraction – the bending of waves as they pass a barrier and part of the wave slows down.

InterferenceWave interference is the phenomenon which occurs when two waves meet while traveling along the same medium. The interference of waves causes the medium to take on a shape which results from the net effect of the two individual waves upon the particles of the medium.

Constructive interference is a type of interference which occurs at any location along the medium where the two interfering waves have a displacement in the same direction.

Destructive interference is a type of interference which occurs at any location along the medium where the two interfering waves have a displacement in the opposite direction.

This "destruction" is not a permanent condition. In fact, to say that the two waves destroy each other can be partially misleading. When it is said that the two pulses destroy each other, what is meant is that when overlapped, the affect of one of the pulses on the displacement of a given particle of the medium is destroyed or canceled by the affect of the other pulse.

Equal waves

Unequal waves

Interference Patterns

http://id.mind.net/~zona/mstm/physics/waves/interference/twoSource/TwoSourceInterference1.html

Locations along the medium where destructive interference continually occurs are known as nodes.

Locations along the medium where constructive interference continually occurs are known as anti-nodes.

Electromagnetic Waves and Spectra

Note the interference pattern caused by the diffraction grating in the picture above.

Q: How do electrons make light?

A: When an electron returns to the ground state from the excited state, the excess energy is given off as a photon of light.

• The position of the electron before and after determines the wavelength of the light.

Electromagnetic Waves

                  What are electromagnetic waves ?

Light, microwaves, x-rays, and TV and radio transmissions are all kinds of electromagnetic waves.

They are all the same kind of wavy disturbance that repeats itself over a distance called the wavelength.

http://www.colorado.edu/physics/2000/waves_particles/index.html

Frequency determines the type of electromagnetic radiation and color in light.

Generally, the light we see is composed of a mixture of wavelengths. White light is composed of red, green, yellow, and

blue photons. We can separate light into its component wavelengths by using a dispersing element, either a prism or a

diffraction grating. Once the light is dispersed, it forms a spectrum. A rainbow is an example of a spectrum (the dispersing elements are water droplets which act as prisms). The plural of

"spectrum" is "spectra".

Raindrops sometimes act as a prism, producing a rainbow.

Sunlight passed through a prism or diffraction grating produces a continuous spectrum.

Prism Diffraction grating

There are 2 basic kinds of spectra: continuous spectra- like a rainbow. line spectra -The light is concentrated into specific colors or wavelengths.

Continuous Spectra of White light:

Line Spectra:

Emission spectra

Absorption spectra

http://hea-www.harvard.edu/~efortin/thesis/html/Spectroscopy.shtml

Light given off by the excited electrons of a particular element give a Bright-line emission spectra. The diffraction grating maybe enclosed in a tube with a slit for light to enter at the opposite end. This device is known as a spectroscope.

This technique is so reliable that scientists can tell what elements they are looking at just by reading the lines. Spectroscopy is the science of using spectral lines to figure out what something is made of. That's how we know the composition of distant stars!

Quantum Theory

Key Terms:

• Valence: The outer most electrons, that is those in the highest energy level.

• Isoelectronic: Having the same electron configuration as another atom.

Sublevels (l ) and Orbitals, (m)

Spin Quantum Number ms

Sublevels (l )

4 Important Rules• Aufbau Principle: Electrons always occupies the

lowest energy orbital possible.• Hund’s Rule: (“Boys on the Bus”): Each orbital in the

same energy level and sublevel must contain 1 electron before the electrons pair.

• Pauli Exclusion Principle: No two electrons in the same atom can have the same set of quantum numbers.

• Heisenberg Uncertainty Principle: It is impossible to know simultaneously both the position and velocity of an electron or any particle.

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Time to Practice!!!

energysublevel

The End