Light

Complimentary Colors

These are any two colors of light that combine to produce white.

Quantum

The smallest type of something. Ex: A penny is the smallest or least in value of American money.

Neils Bohr

A Danish physicist who made foundational contributions to understanding atomic structure. He came up with the "Planetary Model" of the atom in 1913. He also documented the spectral lines of many different gases.

Christian Huygens

A Dutch scientist and mathematician. He invented the Huygens' Principle. Supported wave theory through reflection. (1629-1695)

Louis de Broglie

A French physics student. He developed the idea of the dual theory of matter and the _____________ wavelength of matter in his Ph. D. thesis in 1924. He stated that particles in matter can sometimes have wave characteristics, but they are just too small to notice.

Ernest Rutherford

A New Zealand-born British physicist who came to be known as the father of nuclear physics. He conducted the gold foil experiment, which led to his discovery of the nucleus which quickly amended Thomson's "Plum Pudding" model of the atom.

Translucent

A material that is not fully transparent and allows light to pass through, but the light does not reemerge unaltered. Ex: stained glass

"Planetary Model"

Bohr made this model of the atom. He proposed a positively charged nucleus surrounded by electrons moving around it in specific orbits like the planets in orbit around the sun. The electric attraction between the nucleus and the electrons provided centripetal force necessary to keep the electrons in orbit. He also calculated that each electron moved in a specific orbital or energy level. As we know today, the electrons don't travel in distinct circular orbitals. This model is also incomplete because it had no neutrons or protons.

Electromagnetic Spectrum

All EM waves have the same structure and move in a give medium, or vacuum, at the same speed. Calling it the "speed of light" is a rather narrow definition of the term as it is the speed of all the other EM waves as well. The only structural difference between all these various EM waves are their wavelength, frequency, and energy. The ___________ is a continuum, meaning that it continues in both directions, increasing in frequency in one direction and in wavelength in the other direction. Remembering that the energy of the wave is directly proportional to the frequency, understand that the EM waves toward the high frequency end of the spectrum will also have higher energies. All these different waves, while having the same structure and speed, are perceived in different ways and have different effects and applications.

J. J. Thomson

An English physicist credited with the discovery and identification of the electron, and with the discovery of the first subatomic particle in 1897. He also came up with the "Plum Pudding" model of the atom, which described atoms as a positively charged mass with negatively charged particles floating inside.

Photon Theory (1)

Einstein applied Planck's quantum theory to light. The frequency of a light wave is a function of the speed of light and the wavelength of light. This is shown in the equation for wave velocity, c = λf. Einstein described light as interacting with matter as though it were a "particle" or photon that had an energy as described by Planck's quantized energy. This was expressed by the photon energy equation, E = hf or E = hc/λ.

Max Planck

He was a German theoretical physicist who originated quantum theory. He observed that when energy interacted with matter, it always seemed to be at discrete multiples of a base value, or quanta. He characterized this energy with the equation E = hf, which was only for photon energy, and also created Planck's constant, h = 6.63 x 10^-34 J(s).

Young's Experiment

If light were indeed a particle, one would expect to see two bands of light on the screen behind the card with the slits, much like paint going through a stencil. Instead, what was seen was a pattern of dark and light bands. As the light passed through the two slits, it diffracts around the edges, creating effectively two separate sources of light in the manner predicted by Huygens' Principle. Then, as the wave fronts from the two separate sources move from the card with the slits toward the screen behind it, they begin to overlap and produce regions of constructive and destructive interference and the pattern of dark bands seen by Young. Suddenly there was now evidence of light exhibiting three of the four main wave characteristics: reflection, interference, and diffraction.

Dual Theory of Matter

It soon was suggested that if if were possible for light to be considered as a particle and having momentum, that it was also possible for matter to be described as having wave properties. Louis de Broglie described that particles of matter, such as electrons, could be shown to have wave characteristics.

Opaque

Materials which do not allow light to pass through them.

Transparent

Media into which light or any other type of wave can pass and reemerge freely or unchanged. In this type of media, light will travel at various speeds, depending on the material.

Primary Colors

Of pigment, these are red, blue, and yellow. Of light, these are red, blue, and green. - The combination of __________ pigments will produce black, but the combination of __________ light will produce white.

Predictions vs Reality

Prediction by EM Wave Theory... - KE should increase with intensity - Frequency should be irrelevant What Actually was Happening... - KE is unrelated to intensity - KE is proportional to Frequency - Below a certain threshold frequency, there will not be any photoelectric effect at all

Structure of Light

Since the propagation of the energy in the light wave is done through the displacement of varying fields rather than the displacement of matter, the presence of a material medium is not necessary. It is the strength of the energy that fluctuates in displacement. In a given medium, the speed of these waves is constant, and these waves vary in terms of wavelength and frequency. The speed is the same as the speed of light, and is equal to the wavelength times the frequency, c = λf. The energy of an EM wave is directly proportional to its frequency and inversely proportional to its wavelength.

Photon Theory (2)

The energy of each photon of light increases as the frequency of the light increases. If the intensity of the light is raised, it only increases the number of photons, not the energy of the photons. The photons interact one-to-one with the electrons in the metal, transferring their energy. It takes a minimum amount of energy for a single electron to be released by a given metal, and the photons must have a sufficiently high frequency (and, therefore, energy) in order to release the electrons. Once that threshold is reached, the kinetic energy of the released electrons will increase as the frequency of light is increased.

Particle Theory

The first widely accepted theory about the nature of light was that light was composed of particles. The acceptance of this idea was in large part due to the support of it by Issac Newton. Newton's "corpuscular theory" stated that light was composed of tiny particles, or "corpuscles".

Issac Newton

The foremost scientist of his day who possessed a great deal of clout and influence over his fellow scientists. He did not hesitate to use his position to attack anyone who disagreed with his ideas. Supported particle theory. (1642-1727)

Radio Waves

These waves are the lowest energy. They have longer wavelengths and lower frequencies than the rest of the spectrum. When a person tunes a radio, the numbers associated with different radio stations are actually the frequencues of the EM waves which carry those stations' broadcasts. The numbers of stations on the FM band correspond to MHz, or millions of cycles per second. On the AM band, the frequencies are measured in khz, or thousands of cycles per second. With FM signals having the higher frequency and therefore the higher energy, those stations are able to produce broadcasts that have certain advantages over AM stations, such as clearer reception and stereo sound. AM, however, can sometimes be received better in mountainous regions where the longer wavelengths can travel around large geographical obstacles more easily tan the shorter wavelength FM signals.

TV Waves

These waves are the second lowest energy on the EM spectrum. Along with radio waves, they have longer wavelengths and lower frequencies than the rest of the spectrum. ________ broadcasts are sent out on waves that have an even higher frequency and energy, as they must accomplish even more than a radio signal.

X-Rays

These waves have enough energy to go right through nearly all human tissue. Depending on the actual frequency, these photons can essentially pass right through a person. If the energy is adjusted so as to not pass through denser tissue, like bone, then they are useful in producing pictures of skeletal systems of people who have been injured. If the photons are made to be even more sensitive, they can be used to detect denser-than-normal tissues such as tumors.

Microwaves

These waves have even higher frequencies and higher energies than most communications EM waves. This portion of the EM spectrum actually overlaps into the infrared spectrum. They also tend to heat the water molecules found in food first.

Ultraviolet Light/Radiation

These waves have frequencies higher than the blue end of the visible spectrum, and accordingly higher energies. Photons of _____________ have enough energy that they can actually penetrate the outer layers of human skin. When they deposit their energy, they can catalyze chemical reaction in the pigments which result in suntan or sunburn. There is a significant amount of sunlight that consists of _______________, but a great deal of it is blocked by ozone, a molecular form of oxygen (O3) in the upper part of the earth's atmosphere.

Gamma Radiation

These waves lie in the x-ray spectrum and are so high in energy that they will essentially burn right through human tissues. These kinds of waves are extremely dangerous and are often produced in nuclear reactions. They can be used in certain types of medical therapy, such as cancer radiation treatments, but they can result in many unwanted side effects and illness.

The de Broglie Wavelength of Matter

This can be determined with the equation λ = h/mv, where m is the momentum of a particle. In order for this to be significantly large, the particle must have a very small mass (because Planck's constant in the numerator is also extremely small). An ordinary-sized object, like a baseball, when moving at a common speed, could be described as having a wavelength, but the length would be ridiculously tiny. An electron, on the other hand, can have a significant wavelength when it is moving, and it can be observed to undergo various wave characteristics, such as diffraction.

White Light

This consists of a wide range of wavelengths, or colors, of light. While many sources of ______________ do contain a complete or nearly complete color spectrum, it actually is not necessary for the entire color spectrum to be present. If there are enough different and varied wavelengths present in a sample of light, they will all combine to form this type of light. When it passes through a prism, the various wavelengths of which it is composed will be separated, showing what colors are actually there. Colors don't disperse through windows because the two sides are parallel.

Michelson-Morley Experiment

This experiment in 1800 finally determined the speed of light as 3 x 10^8 m/s. It also established the idea that the speed of light is slower in water than in air. This was one of the final things in the Physics world that fully went against Newton's particle theory, and now everyone was convinced that light was a wave.

Pigment

This is a chemical that will absorb other wavelengths except for the ones it reflects, so that we see an object as being that color. It is referred to as "subtractive". The more colors of this that are combined, the closer the color gets to black, because more light is being absorbed and fewer wavelengths are being reflected. Ex: Mixing many colors of paint together only leaves you with a dark black color.

Polarizing Filter

This is a device which only allows light which is oscillating in one plane to pass through it. This could be likened to a piece of cardboard with a slit cut in it that has a rope running through it. If a transverse wave is sent down the rope, it will only be able to pass through the cardboard if the orientation of oscillation of the rope is parallel to the slit in the cardboard. Any waves oscillating in an unparallel plane would be blocked when they reached the cardboard.

Huygens' Principle

This is a technique used for predicting the future position of a wave when an earlier position is known. It states that every point on a wave front can act as an individual source itself. If you algebraically add together all the individual wave fronts coming from each individual point (there would be an infinite number of points), the sum is just the next larger wave front.

Refraction

This is a wave characteristic, but Newton used it to support his particle theory of light. Experiment: As a marble rolls across a level surface and then reaches a ramp, it will change velocity as it rolls down the ramp. If it strikes the top of the ramp at an oblique angle, it will change direction and roll toward the normal in its path down the ramp. Newton likened this to the same change in direction as light moving from air into water. The flaw in this argument was that it assumed that light went faster as it moved from air to water; it actually slows down, but no one knew the speed of light at this time.

Orientation of Oscillation

This is known as the direction in which the medium is being displaced. Of course, with an EM wave, there is not medium being displaced, but the electric and magnetic fields are fluctuation in specific directions at certain angles. The ______________ of an EM wave could be vertical or horizontal or any angle in between

Unpolarized Light

This is light from a source that does not have any particular plane of oscillation. Not only does this light not have any particular orientation of oscillation, it also tends to be oscillating in many different planes or at many different angles. Almost all light sources are this.

Polarized Light

This is light in which all the waves are indeed oscillating in the same plane. Reflected light tends to be this (at least partially) parallel to the plane of the surface off which it reflects as well.

Visible Spectrum

This is often characterized by the acronym ROY G BIV. This order progresses from lower frequency and lower energy to higher frequency and higher energy. When an object starts to get hot, it first begins to radiate red light. But if it gets hotter, assuming it doesn't catch on fire ore melt, it can eventually produce wavelengths all along this spectrum, causing it to appear "white hot". Many objects will burn before this happens, such as wood. Remember the hottest part of the flame is the blue rather than the red/orange. Our eyes can detect EM radiation, but only within a certain range of frequencies, the ___________________.

Light

This is referred to as "additive". The more wavelengths of this that you combine, the closer the color gets to white. Ex: A red shirt looks red because there are wavelengths of red ________ that are entering our eyes from the shirt.

Work Function

This is the minimum energy necessary to release an electron from a given metal, and it is a constant that depends on what metal is being used. The kinetic energy of the released electrons can thus be predicted by subtracting the energy of the work function from the energy of the incident photons. This is proven by the equation, E = KE + Wo.

Scattering of Light

This is the process when gas molecules in the earth's atmosphere knock out the wavelengths of light that most correspond or are similar to the diameters of those molecules. The earth's atmosphere is composed of mostly nitrogen gas (N2) and oxygen gas (O2), and the diameters of these molecules are very nearly the size of the wavelengths of blue light that we see in the sky. As a nearly full spectrum of white light from the sun passes through our atmosphere, these blue wavelengths are knocked our of the path of the light at 90 degree angles. It is not a coincidence that blue and yellow are complimentary colors. If the molecules in our atmosphere were a different size, particularly larger, our sky might appear to be a different color than blue.

Photoelectric Effect

This is where certain metals under the illumination of a light source can produce an electric current.

James Clerk Maxwell

This physicist is best known for his creation of the electromagnetic theory. He also predicted the speed of light mathematically and got it correct.

Retinal Fatigue

This process occurs when our brain begins to ignore a certain wavelength of light. This happens when you stare at a color for too long. When you turn your gaze away, you will see the complimentary color. This is a product of having a nervous system that relies heavily on new stimuli from the world around us. When we continually get the same stimulus to a nerve for a long period of time, our brain tends to start ignoring that stimulus until is somehow changes.

Albert Einstein

This scientist wrote a paper in 1905 explaining the photoelectric effect and why is happened, which revolutionized the way in which we consider light and matter. He received the Nobel Prize for his explanation of the photoelectric effect and development of the Photon Theory. He is also the most famous of all the physicists.

Dual Theory of Light

This simply says that light is not necessarily a wave or a particle, but that it has characteristics of both. It was shown that light did indeed behave like a wave as it traveled from place to place, but tended to behave more like a particle when it interacted with matter. Einstein's photons can even be described as having momentum like any other particle, which is mass times velocity, but they can't be slowed to a stop to measure their mass at rest.

Infrared Light/Radiation

This type of light is between microwaves and visible light waves in the EM spectrum. This radiation is very important to maintaining the thermal balance of the earth, as well as aiding various nocturnal animals. While humans cannot see these waves, many animals can. When objects are hot, but not hot enough to radiate red light, they will emit _________________. Anything that has heat emits ________________.

Electromagnetic Waves

This type of wave does not need a medium in order to propagate, but they can move through various materials. They are also transverse waves, although in a much more complicated way than transverse waves traveling through a rope. They consist of two different components, a fluctuating electric field an a fluctuating magnetic field. The two fields vary in phase with each other in perpendicular planes.

Spectral Lines

When a gas is placed in a vacuum tube and placed across a large electric voltage, the gas will emit light. The light emitted is unique to each gas. While the difference may not be noticeable to the naked eye, if the light is passed through a prism, one will see not a continuous spectrum (as with most white light sources), but only very specific lines - specific wavelengths of light which are particular to each gas. These are like fingerprints by which these gases can be identified. No one was able to tell why each gas had a specific set of lines until Neils Bohr.

Index of Refraction

While the speed of light c is constant in a vacuum, it will slow down from that speed as it travels through various materials. The speed v, will always be slower than c, the speed of light in a vacuum. The ratio of the speed of light in a vacuum compared to the speed of light in a certain material is called _____________. It is shown by the equation n = c/v. Different materials will have different ___________, depending on how much light slows down when traveling through those materials. This will always be larger than 1, since light will never move faster than c.

Reflection

While this is generally thought of as a wave characteristic, Newton argued that particles could behave in the same way if they were small enough and moving very fast. The smaller the particle, the less gravity would affect its path as it bounced. Light, of course, would be composed of extremely small particles, and they would be moving very fast.