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Transcript of WAVES
(a) long waves
(b) medium waves used by AM station
(c) VHF (very high frequency) used by FM stations
(d) ULF (ultra high frequency) used by police radio communication, military aircraft, and television transmissions.
- is a disturbance traveling through a medium or in a vacuum.
JAMES CLERK MAXWELL predicted the existence of electromagnetic waves
- a succession of periodic disturbances
Waves are classified according to:
their direction of propagation
can travel in vacuum and in material media.
light, heat waves, radio waves, microwaves
require a material medium to propagate.
sound wave (we all know that sound cannot travel in a vacuum)
is one in which the particles of a medium are vibrating PERPENDICULARLY to the direction of wave propagation
are made up of of alternating hills and valleys
is one in which the particles of the medium vibrate PARALLEL to the direction of the wave propagation.
trough - bottom of the valley
crest - top of the hill
compressions - where the particles of a medium are CLOSER together
rarefactions - where they are farther apart
travel through the earth's interior
are divided into primary wave/P waves (longitudinal), and secondary wave/S waves (transverse).
travel at a surface
are further classified into Love waves and Rayleigh waves
Love waves - named after A. E. H. Love
- the fastest surface waves
Rayleigh waves - named after Lord Rayleigh
- are responsible for the shaking felt during an earthquake
- have both longitudinal and transverse properties
- generated by earthquakes or explosion
-are produced by oscillating electrical charges with the electric field and magnetic field vibrating perpendicularly to each other and to the direction of the wave propagation
- are transverse waves
They all propagate through a vacuum or air with the same speed equal to 3 x 10 m/s.
History of Electromagnetic Waves
However, it was not until 1887,
through the efforts of HEINRICH HERTZ, when those waves (except light) were observed to existence.
Electromagnetic waves are classified according to their:
- is a term used to describe the entire range of electromagnetic radiations arranged in order of their frequencies or wavelengths
- special names are assigned to these waves
The following are the regions in the electromagnetic spectrum:
- discovered by HEINRICH HERTZ (1887)
- Extraterrestrial sources of radio waves:
SUN and the planet JUPITER
- are EXTREMELY HIGH frequency radio waves
- are the LONGEST of all the electromagnetic waves
ranging from 10 m to 10 m
- credited to JAMES CLERK MAXWELL (1864)
- SHORT wavelengths ranging from 10 m to 10 m
- known to cause CATARACT, so pressing one's face against a microwave oven to see if the food is cooked already is not a good habit.
- very easily absorbed by water molecules. That's why they are used in microwave ovens.
- have longer wavelengths than red
- wavelengths ranging from 7 x 10 m to 10 m
SIR WILLIAM HERSCHEL identified these rays around 1800
- also known as HEAT WAVES
- used in remote controls for televisions, burglar alarm systems, and night visions
Physiotherapists use heat lamp to heal sports injuries.
Too much exposure to infrared rays can lead to overheating.
- is the part of the electromagnetic spectrum visible to our unaided eye
- extends from the short-wave violet to the long-wave red.
The ffg. are the approximate wavelengths of different colors of light:
Violet 410 nm
Blue 470 nm
Green 550 nm
Yellow 590 nm
Orange 610 nm
Red 760 nm
In modern usage, indigo is not usually distinguished as a separate color.
Ultraviolet Rays (UV Rays)
- discovered by JOHANN WILHELM RITTER
- wavelength ranging from 6 x 10 m to 4 x 10 m.
- major source is the SUN
- good source of Vitamin D
- used to sterilize medical equipment
- can cause skin cancer
- can damage the retina
(that's why we use sunglasses)
X-Rays (Roentgen Rays)
- are a thousand times shorter than the shortest visible light
- accidentally discovered by WILHELM CONRAD ROENTGEN while working on cathode-ray tubes, which made him awarded the first Nobel Prize in Physics
- wavelengths ranging from 10 m to 10 m
- used to take photographs of our internal body parts, and to check your luggage in the airport
- can cause cancer and damage tissues
- are given off by radioactive materials like Cobalt-60 and Cesium-137
- are highly penetrating because of their VERY SHORT wavelengths ranging from less than 10 m to 10 m
- used to detect crack on metals
- can cause cancer and even mutation
- used to destroy cancer cells in a process called RADIOTHERAPY
- credited to PAUL VILLARD in 1900
All waves exhibit refraction, reflection, diffraction, interference, and the Doppler effect. In addition, transverse waves demonstrate polarization.
Refraction and Reflection
REFRACTION - refers to the change in direction and change in wavelength or velocity of the wave that occurs as the wave is transmitted from one medium to another.
REFLECTION - is the turning back of a wave to the original direction it is traveling upon hitting an object
Diffraction - demonstrates Huygen's principle
HUYGEN'S PRINCIPLE states that every point on a wave can act as a new source of waves.
Because of diffraction, sound can be heard around the corners of a building.
MAX VON LAUE discovered the diffraction of X-ray by crystals in 1913. This phenomenon is useful in studying the structure of crystals.
Interference - the combination of waves passing the same medium at the same time
According to the SUPERPOSITION PRINCIPLE, when two or more waves travel simultaneously in the same medium , each wave will proceed independently of the others.
The resulting disturbance is the sum of individual waves.
Interference may be constructive, partially destructive, or totally destructive.
happens when two wave of the same frequency, in phase, and traveling in the same direction.
The resulting wave is of the same frequency but with an amplitude equal to the sum of the amplitudes of the two component waves.
PARTIAL DESTRUCTIVE INTERFERENCE
happens when the above mentioned waves have different amplitudes.
The resultant waves an amplitude equal to the difference of the amplitudes of the component waves.
- a special case of interference
- the case of two waves of the same frequency, the same amplitude, in phase, but traveling in opposite direction
The result is a standing pattern consisting of nodes and antinodes.
NODES - are regions where the particles of the medium are not displaced from their equilibrium position
ANTINODES - are regions of maximum displacement
- are formed when we pluck the strings of a guitar
The Doppler Effect
- named after CHRISTIAN DOPPLER, who first thought of the idea in 1842 for sound waves
- the apparent change in the frequency of the source of a wave due to the motion of source and/or observer
- doppler effect on light
- is expressed in terms of color rather than frequency change
blue shift - increase in frequency. Frequency INCREASES as we move toward the BLUE part of the spectrum
red shift - decrease in frequency. Frequency DECREASES as we move toward the RED portion of the light spectrum
- special kind of radar
- used in forecasting and detecting planes
- is peculiar to transverse waves only
- is a test to determine whether a wave is transverse or not
A wave is said to be polarized if its vibrations are confined in only one plane.
- is said to occur when an object vibrates at its natural frequency upon receiving impulses from a source vibrating at the natural frequency of the object.
NATURAL FREQUENCY - a characteristic frequency where all objects have a tendency to vibrate at
The result of resonance is a wave of greatly increased amplitude on the part of the object
GOOD EFFECTS OF RESONANCE
By means of resonance, we are able to tune in to our favorite radio station.
Resonance is used in some medical imaging.
Musical instruments produce overtones because of resonance.
BAD EFFECTS OF RESONANCE
In 1831, cavalry troops marching across a bridge in Manhattan, England were able to set up resonant vibration in the bridge to the point of destroying it.
On November 7, 1940, at around 11:00 a.m., the four-month-old Tacoma Narrows Bridge in Washington collapsed because of wind-generated resonance.
Resonance due to shaking of the ground during an earthquake may also cause a building to crack or collapse.
by: Claire Anne P. Luces
III-Faraday S.Y. 2013-2014