Electromagnetic Radiation
Maxwell found that the speed of an electromagnetic wave would be
3 times 10 to the 8th power, the speed of light, in order for the mutual induction of electric and magnetic fields would occur indefinately with neither a loss or gain in energy
Since the speed of light is 300,000,000 meters per second, an electric charge oscillating once per second will, or 1 hertz frequency, will produce a wave with a wavelength of
300,000,000 meters long. This is due to the fact that only one wavelength is generated in 1 second.
In water, light travels
75% of the speed of light and about 67% of the speed of light through glass
electromagnetic waves
A wave that consists of vibrating electric and magnetic fields. These waves transfer energy
When light is reflected by a mirror, light composed of a stream of particles would bounce away or are reflected from the smooth surface
Because the particles are very tiny, a huge number are involved in a propagating light beam, where they travel side by side very close together
Evidence that light is a wave: Diffraction
Diffraction occurs when light spreads out when it moves through an opening or past a barrier
Evidence that light is a wave: Doppler Effect
Doppler Effect is when the frequency of light changes when the source of the light wave is moving
Formula relating mass and energy
E=mc^2 Energy of the particle equals mass times the speed of light squared
Christiaan Huygens
Huygens postulated that the more the light was bent or refracted by a substance, the slower it would move while traversing across a substance. Light is composed of waves
Upon impacting the mirror, the particles bounce from different points, so their order in the light beam is reversed upon reflection to produce a reversed image
If the surface is very rough, the particles bounce away at a variety of angles, scattering the light
Why is glass transparent to visible light?
In the range of visible light, the forced vibrations of electrons in the glass are at smaller amplitudes, the vibrations are more subtle. So, re-emission of light rather than the generation of heat occurs, and the glass is transparent.
Evidence that light is a wave: Interference
Interference occurs when light waves combine to create a pattern of bright and dark areas
What is visible light used for?
Light bulbs, laser pointers, telescopes
Evidence that light is a wave
Light has no mass
Sir Isaac Newton
Light was composed of a steady stream of particles; the particles proceeded in a straight line,until it was reflected, refracted, diffracted, or disturbed in another way
Why is glass not transparent to infrared light?
Lower frequency infrared causes whole molecules, rather than electrons, to resonate, and again heat is generated and the glass is opaque
Evidence that light is a wave: Photoelectric effect
Photoelectric effect occurs when shining a light on certain types of metal causes electrons to be released from the atoms in that metal
Evidence that light is a wave: Polarization
Polarization is when light can be filtered to vibrate in a specific direction
What are radio waves used in?
Radio communication, TV broadcasts, radio telescope on Earth
Evidence that light is a wave: Refraction
Refraction occurs when light bends when it enters a new medium
An electron further from the nucleus has greater potential energy because the positively charged nucleus is attracted to the negatively charged electron.
So, these two opposite charges will want to move close to one another due to their attraction. The further away the electron is, the more it will want to move closer to the nucleus, giving it more potential energy.
where are gamma rays found in nature?
Solar flares, explosions from nuclear weapons, radioactive substances, gamma ray bursts
where are infrared waves found in nature?
Sun, stars, animals, green plants
where are visible light waves found in nature?
Sun, stars, fire
where are radio waves found in nature?
Sun, stars, sparks, lightning
What are infrared rays used for?
TV remote controls, food warming lamps, satellite weather photography, night vision scopes, computers
What are ultraviolet waves used for?
Tanning booths, security identification, sterilizing equipment
Why is glass not transparent to ultraviolet light?
The natural frequency of vibration for electrons in glass is the same as the frequency of the ultraviolet light, making the resonance in the glass occur when ultraviolet waves shine on it. The energetic vibrations of electrons generate heat instead of wave re-emission.
If light were composed of particles, the particles entering the second medium would be refracted and pass through in a linear pathway. When the second boundary is encountered, the particles travel back into space at a medium
The particle theory has a difficult time explaining why particles of light should change their direction when they pass through one medium and into another
The magnitude of the constant speed of electromagnetic waves is a consequence of what?
The underlying principle that dictates the speed of light and other electromagnetic waves is the conservation of energy
Is light a wave or a particle?
This is called wave-particle duality.
Photoelectric effect
Under circumstances, light could dislodge electrons from the atoms of several metals
Destructive interference
Waves that meet out of step will cancel each other out
How long does it take for a far away electron to know that a change in fields has occurred?
What is the speed of the wave?
Particle and wave refraction
When a beam of light travels between two media having differing refractive indices, the beam undergoes refraction and changes direction when it passes into the second medium
Young's double slit experiment
When light waves from a set of two slits are spread, or diffracted, they meet and over lap. In some cases, the overlap combines the two waves or out of step with each other
What are x rays used for?
X-rays for medical diagnosis, Cat scan machines, airport scanners
In what ways is walking through a room and light going through glass not analogous?
You are the one who begins and ends the walk. Contrastingly, light absorbed an electron in a transparent material is not the same light that is re-emitted
Because of the magnetic field surrounding the bar magnet,
a magnet is able to exert a force on objects without touching them. In order for an object to feel the force of a magnetic field, they have to be located in that magnetic field.
A photon is
a packet of energy, or a particle that is given off when an electron returns to a lower energy level
After being diffracted, the light that is recombined by interference produces
a series of bright and dark fringes along the length of the screen
With the diffraction of particles, the particles produce
a straight shadow. This is because the light particles were said to always travel in straight lines. If the particles encounter the edge of a barrier, they will can not spread out behind the edge
Light is a particle in the fact that it is
a train of particles, or photons, moving at the speed of light
Evidence that light is a particle: Light ca travel through
a vacuum, or empty space
In developing his quantum theory, Einstein suggested that electrons attached to atoms in a metal can
absorb a specific quantity of light, or a photon, and thus have the energy to escape
opaque materials
absorb light without re-emission
Light originates from the
accelerated motion of electrons
Electromagnetic waves are transverse waves that can travel
across space without a medium. When the waves strike matter, they may reflect, refract, or diffract, or they may be converted to other forms of energy
AN electromagnetic wave begins when
an electrically charged particle vibrates
The vibrating electric and vibrating magnetic field combine to create
an electromagnetic wave
The vibrating electric and magnetic fields regenerate each other to make up
an electromagnetic wave, which emanates (moves outward) from the vibrating charge
Unlike a mechanical transverse wave, which requires a medium, electromagnetic waves
are able to travel through empty space. No energy is lost, and the wave does not get weaker as it travels
The speed of light through a vacuum is 3 times 10 to the 8th power, but the light travels a slight bit less than this in the
atmosphere
Depending on the wavelength of the light, it is going to
bend a different amount
diffract
bend around objects
refract
bend when travelling through different materials
Louis- Victor de Brogile proposed that all matter and radiation have properties that resemble
both a wave and a particle
reflect
bounce back
What are microwaves used for?
cell phones, microwave ovens, radar, microwave telescopes
A changing magnetic field induces a
changing electric field. The changing electric field induces a changing magnetic field
With lower frequency waves striking the glass, the atoms and molecules holds the energy for less time, with less chance of
collision with neighboring atoms or molecules, and less energy is transformed into heat. The energy of vibrating electrons is re-emitted as light
an electromagnetic wave is a wave that
consists of both electric and magnetic fields
The speed of light is always a
constant
For a specific wavelength of light, like blue, the electrons produced a
constant potential, or a fixed amount of energy
The photon that is released as it goes to a lower energy level is a
corpuscle of pure energy- a particle of light, which is ejected from the atom
Decreasing or increasing the amount of light, produced a
corresponding increase or decrease in the number of electrons liberated, but each still maintained the same energy. In other words, electrons escaping their atomic bonds had energies that were dependent on the wavelength of light, not the intensity
If an atom is excited, many frequencies of light are emitted as each frequency corresponds to
different energy levels excited and de-excited within it. These frequencies combine to give a characteristic color of light from each excited element
Light travels at different average speeds through
different materials
Different frequency waves results from
different wavelengths. Low frequencies produce waves of long wavelengths.
As the electromagnetic wave travels away from the source, the energy is
diluted as it spreads out over an ever larger area. This is like a sound wave, which spreads out and becomes less intense farther from the source
The electric and magnetic fields are also at right angles to the
direction that the wave travels
The electric and magnetic fields come at right angles to
each other and to the direction that the wave is moving
An EM wave starts with a vibrating charge, creating a vibrating
electric and magnetic fields
An electron farther from the nucleus has a greater
electric potential energy with respect to the nucleus than an electron near the nucleus
An electric field is an area of
electrical force surrounding a charged particle. Similar to a magnetic field, an electric field can exert force on objects over a distance without actually touching them
An electromagnetic wave begins when an
electrically charged particle vibrates
If you shake an electrically charge rod in empty space,
electromagnetic waves are produced. This is due to the fact that the moving charge is actually an electric current. A magnetic field surrounds a changing electric current
Since the electric and magnetic fields are at right angles to each other,
electromagnetic waves are transverse waves
Light is carried in an electromagnetic wave that
emanates, or moves outward from a vibrating electrons in atoms
Electromagnetic waves can travel through
empty space. Mechanical waves, however, absolutely require a medium to propagate
All electromagnetic waves move at the same speed through
empty space. They travel at the speed of light
The higher the frequency, the higher the
energy
As a mechanical wave needs a medium to propagate,
energy is lost and the wave gets weaker as it travels
The fields contain energy acquired from the vibrating charge. If the field disappeared with no means of transferring energy to other forms,
energy would be destroyed. So, too low of an emanation of electric and magnetic fields does not agree with the law of energy conversion
If emanation speeds were immensely high, the electric and magnetic fields would be induced to greater and greater magnitudes, with a crescendo of
ever increasing energies, not agreeing with the law of energy conversion
When light is incident upon matter, some of the electrons in the matter are
forced into vibration
The amount of energy in a photon may vary. It depends on the
frequency of the electromagnetic radiation
The way in which a receiving material responds when light is incident upon it depends on the
frequency of the light and the natural frequency of the electrons in the material
The frequency of the re-emitted light that is passed from molecule to molecule is identical to the
frequency of the light that produced the vibration in the first place. The principle difference is a slight time delay between absorption and re-emission.
The frequency of the wave is the same as the
frequency of the vibrating source
where are microwaves found in nature?
gas clouds collapsing into stars
Visible light is the only section of the electromagnetic spectrum that is visible to the
human eye
At a specific speed, mutual induction of electric and magnetic fields would continue
indefinately, with neither a loss or gain in energy
Infrared waves, with frequencies lower than visible light, vibrate the electrons and entire molecules of the glass. The vibration of electrons and molecules increases the
internal energy and the temperature of the structure, which is why infrared waves are often called heat waves.
Magnetic and electric fields are
invisible areas of force surrounding magnets and charged particles
When an electron falls to a lower orbit,
it releases energy in the form of light. The atom loses its temporarily acquired energy when the electron returns to a lower energy level and releases this energy as radiant energy. The electron has undergone excitation and de-exciteation
When light emerges from these materials and into the air,
it travels at its original speed c
The frequency of the photon is directly proportional to
its energy. A photon in a beam of red light, for example, carries an amount of energy that corresponds to its frequency. A photon of twice the frequency has twice as much energy
With a higher frequency and higher energy, the photons have a better ability to
knock off electrons, or do what ever they need to do
Huygens suggested that if light were composed of a stream of particles, then the more the light was bent, the faster the light would move through the material because
light entering a denser medium would be attracted by molecules in the medium and would experience an increase, rather than a decrease in speed
Transparent materials such as glass and water allow
light to pass through in straight lines. They are transparent to light
The time difference between absorption and re-emission results in a
lower average speed of light through a transparent material
An EM wave is made up of
magnetic and electric fields
Electromagnetic waves act in a similar way to how mechanical waves act in the presence of
matter
Electromagnetic waves can travel through
matter and across empty space
Light does not need a
medium, it will travel fastest through a vacuum. The speed of light is the fastest speed possible
Leonard used a prism to split white light into its component colors, and then selectively focused each color on to a
metal plate to expel electrons
If light were composed of waves, refracting would suggest that a small portion of each angled wavefront should impact the second medium while the rest of the wave is still travelling in the first medium, but will
move more slowly due to the higher refractive index of the second medium. Because the wavefront is now travelling at two different speeds, it will bend into the second medium, thus changing the angle of propagation
The electric and magnetic fields that make up an electromagnetic wave are positioned so that they
occur at right angles to one another
The waves in the electromagnetic spectrum differ from
one another in their frequency
Electromagnetic radiation is a form of energy that is produced by
oscillating electric and magnetic disturbance, or by the movement of electrically charged particles travelling through a vacuum or matter
The frequency of the electromagnetic wave as it vibrates through space is identical to the frequency of the
oscillating electric charge that is generating the wave
With matter, electromagnetic waves can be converted to
other forms of energy. In a microwave oven, for instance, the microwaves strike food and are converted to thermal energy, which heats the food
If a beam of light is allowed to impact a polarizer, only light rays orientated
parallel to the polarizing direction are able to pass through them. If a second polarizer that is the same is positioned behind the first, the light rays would pass through the second polarizer as well
Polarizing filters have a unique molecular structure that allows only light having a single orientation to
pass through.
If the second polarizer is rotated so that it is perpendicular to the first polarizer, none of the light that
passed through the first pass through the second
The energy the atom receives when ultraviolet rays shine on glass may be
passes on to neighboring atoms by collisions or it may be re-emitted
Only waves with a transverse component parallel to the
polarizing filter will pass through, and all others will be blocked
What are gamma rays used for?
radiation treatment for cancer, radiactive tracers for medical tests, equipment to sterilize,
The change of electric and magnetic fields take a certain amount of time to
reach specific particles or electrons
Radio waves allow the radio to
reach the car, cell phones, and communicate with cell towers
With the presence of matter, electromagnetic waves may
reflect (bounce back), refract (bend when travelling through different materials, or diffract (bend around objects)
The visible wavelengths of higher frequencies, like violet and blue, get
refracted more than the low frequency wavelengths
Infrared radiation are what the body
releases
As an electrons returns to a lower energy level, it
releases a packet of energy, or a photon
With polarization, the particle theory does not explain how light is blocked by the
second polarizer
X rays allow people to
see through soft materials and just see the bone
When a light wave is incident upon electrons, which are attached to atoms, the electrons are
set into vibration
As the white light is shone on to the prism, it
slows down as it enters the glass, and it bends
Huygens suggested that if waves consisted of particles, then when two beams were crossed,
some of the particles wold collide with each other to produce a deviation, the amount by which a single measurement differs from a fixed value. This is not the case, however.
In a vacuum, all electromagnetic waves move at the same
speed
Light as waves speculates that a light source emits light waves that
speed in all directions
The strength of the induced electromagnetic wave from the vibrating charge depends on the
speed of emanation, or the electromagnetic wave moving outwards
where are x rays found in nature?
stars, nebulae, radioactive materials
Polarizing particles does not
stop the particles. So, this does not relate to how light works
A high speed changing magnetic field induces a
stronger electric field than a low changing magnetic field. A high speed changing electric field induces a stronger magnetic field
The natural vibration frequencies of an electron depend on how
strongly the electrons are attached to its atom or molecule
where are ultraviolet waves found in nature?
sun
Ultraviolet radiation is from the sun and causes
sunburns
gamma rays are
super high energy!
A common bar magnet exerts magnetic force in an area that
surrounds it, called a magnetic field
Many other sources of electromagnetic waves that people use depends on
technology. Electromagnetic waves are used for communication, cooking, medicine, and many other purposes
Upon impacting a mirror, the waves are reflected according to
the arrived angles, but with each wave turned back to front to produce a reversed image
The farthermost electrons are at a higher energy state, or higher energy level. When an electron is raised to a higher orbit,
the atom is excited. The electron's higher level is only momentary, for it soon returns to its stable state
Resonating atoms in glass can hold on to the energy of the ultraviolet light for a long time. During this time,
the atom makes about 1 million vibrations, and it collides with neighboring atoms and gives up its energy as heat. So, glass is not transparent to ultraviolet light
White light contains all of the visible wavelengths. When white light is projected on to a prism,
the different wavelengths of light get refract differently as it goes through the prism
If the electric charge is set into a vibration with a frequency that includes the visible light spectrum,
the electromagnetic wave will activate the electrical antennae in the retina of the eye. The lower frequency waves appear red and the higher frequency appears violet.
An electromagnetic wave is a transverse wave because
the magnetic and electric fields that make up the wave are perpendicular to the direction of the wave
The higher the frequency of the electromagnetic radiation,
the more energy a photon has
The faster the electric and magnetic fields move outward from the vibrational charge,
the stronger the induced magnetic or electric fields will be induced
The most important source of electromagnetic radiation on earth is from
the sun, which provides all energy that supports life on earth
electromagnetic radiation
the transfer of energy by waves through matter or a vacuum
Electromagnetic radiation
the transfer of energy by waves travelling through matter or across empty space
The Polarization of wave and particles served as evidence for
the wave theory
The diffraction of waves and particles supports
the wave theory
With the diffraction of waves,
the waves bend into the shadow of the barrier
Metals are opaque. However, the outer electrons of atoms in metals are not bound to any particular atom. The electrons are free to wander with very little restraint through the material. When light shines a metal and sets these free electrons into vibration,
their energy does not spring from atom to atom in the material, but the light is reflected. This is why metals are so shiny
If the energy of a photon were inversely proportional to the wavelength,
then shorter wavelengths would produce electrons having higher energies. Einstein's theory was solidified by Campton, who demonstrated that photons had momentum, supporting the theory that matter and energy are interchangeable
When electromagnetic waves strike matter,
they interact with it in the same ways that mechanical waves interact with matter.
Electrons dropping from higher to lower energy levels in an excited atom emit with each jump a
throbbing pulse of electromagnetic radiation called a photon, the frequency of which is related to the energy transition of the jump.
Pretend that while you walk across a room, you make several monetary stops along the way to greet people. This is similar to the way in which light travels through glass because the speed of light travelling through glass is lower because of the
time delays in interactions with atoms along its path
When an electron returns to a lower energy level, it is thought to give off a
tiny packet of energy called a photon
The effects observed with polarized light were critical to the development of the concept that light consists of
transverse waves having components that are perpendicular to the direction of propagation. Each of the transverse components must have a specific orientation direction that enables it to either passes through or be blocked by the polarizer
In opaque materials, vibration given by light to their atoms and molecules are
turned into random kinetic energy into internal energy. The objects become slightly warmer.
When a charged particle vibrates, it causes the electric field around the particle to
vibrate as well
An electromagnetic wave consists of
vibrating electric and magnetic fields
A vibrating charged particle generates
vibrating electric and magnetic fields. These vibrating fields are what make up an electromagnetic wave
A vibrating electric field around the particle creates a
vibrating magnetic field
At lower wave frequencies, like those of visible light, electrons in the glass are forced into
vibration, but at less amplitude.
The strength of the induced electric and magnetic fields depends on the
vibrational rate of the charge, the motion of the electric and magnetic fields, and how fast the electromagnetic wave is moving outward from the vibrating charge
Glass is transparent to
visible light, but not to ultraviolet and infrared light
Microwaves vibrate
water molecules in food so that it heats up
When ultraviolet rays shine on glass, resonance occurs as the
wave builds and maintains a large amplitude of vibration between the electron and the atomic nucleus.
The particle and wave refraction supports the
wave theory
The photoelectric effect is contrary to what would be suggested by the
wave theory
The higher the frequency of the vibrating charge, the shorter the
wavelength of radiation. So, the frequency of a vibrating charge would produce a higher frequency of the radiation
Gamma rays have the highest frequency and the shortest
wavelength. Gamma rays also have the most energy
Even though all electromagnetic waves have the same speed, they can have different
wavelengths and frequencies
Light is a wave in the fact that it has
wavelengths and frequencies
Radio waves have the lowest frequency and the longest
wavelengths. Radio waves have the least energy
Electromagnetic waves behave like
waves and particles
Shake the end of a stick back and forth in still water, and you'll produce
waves on the water's surface
If the speed of emanation is low, or the speed at which the electromagnetic wave travels outward is low, the strength of the induced field is
weak
Constructive interferene
when waves meet in step, they add together
Too low of a speed would mean that the mutual induction of the electric and magnetic fields
would die out
