The scientific Method - body of techniques for investigating phenomena, acquiring new knowledge, or
correcting and integrating previous knowledge
5. Reproducibility (Someone else can repeat the experiment)
Electromagnetic radiation (often abbreviated E-M radiation or EMR) is a phenomenon that
takes the form of self-propagating waves in a vacuum or in matter. It consists of electric and
magnetic field components which oscillate in phase perpendicular to each other and
perpendicular to the direction of energy propagation. Electromagnetic radiation is classified into
several types according to the frequency of its wave; these types include (in order of increasing
frequency and decreasing wavelength): radio waves, microwaves, terahertz radiation, infrared
radiation, visible light, ultraviolet radiation, X-rays and gamma rays. A small and somewhat
variable window of frequencies is sensed by the eyes of various organisms; this is what we call
the visible spectrum, or light.
EM radiation carries energy and momentum that may be imparted to matter with which it
Wave propagation is any of the ways in which waves travel.
Oscillation is the repetitive variation, typically in time, of some measure about a central value (often a
point of equilibrium) or between two or more different states.
vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much
less than atmospheric pressure
The electromagnetic spectrum is the range of all possible frequencies of electromagnetic
radiation. The "electromagnetic spectrum" of an object is the characteristic distribution of
electromagnetic radiation emitted or absorbed by that particular object.
The electromagnetic spectrum extends from below frequencies used for modern radio to gamma
radiation at the short-wavelength end, covering wavelengths from thousands of kilometers down
to a fraction of the size of an atom. The long wavelength limit is the size of the universe itself,
while it is thought that the short wavelength limit is in the vicinity of the Planck length, although
in principle the spectrum is infinite and continuous.
EM waves are typically described by any of the following three physical properties: the frequency f,
wavelength λ, or photon energy E.
EM radiation is classified by wavelength into radio wave, microwave, infrared, the visible region we
perceive as light, ultraviolet, X-rays and gamma rays. The behavior of EM radiation depends on its
wavelength. When EM radiation interacts with single atoms and molecules, its behavior also depends on
the amount of energy per quantum (photon) it carries.
A tachyon is a hypothetical subatomic particle that travels faster than the speed of light.
Our eyes are sensitive to light which lies in a very small region of the electromagnetic spectrum
labeled "visible light". This "visible light" corresponds to a wavelength range of 400 - 700
nanometers (nm) and a color range of violet through red. The human eye is not capable of
"seeing" radiation with wavelengths outside the visible spectrum. The visible colors from
shortest to longest wavelength are: violet, blue, green, yellow, orange, and red. Ultraviolet
radiation has a shorter wavelength than the visible violet light. Infrared radiation has a longer
wavelength than visible red light. The white light is a mixture of the colors of the visible
spectrum. Black is a total absence of light.
Earth's most important energy source is the Sun. Sunlight consists of the entire electromagnetic
The visible violet light has a wavelength of about 400 nm. Within the visible wavelength
spectrum, violet and blue wavelengths are scattered more efficiently than other wavelengths. The
sky looks blue, not violet, because our eyes are more sensitive to blue light (the sun also emits
more energy as blue light than as violet).
The visible red light has a wavelength of about 700 nm. At sunrise and sunset, red or orange
colors are present because the wavelengths associated with these colors are less efficiently
scattered by the atmosphere than the shorter wavelength colors (e.g., blue and purple). A large
amount of blue and violet light has been removed as a result of scattering and the longwave
colors, such as red and orange, are more readily seen.
Energy with wavelengths too short for humans to see
Energy with wavelengths too short to see is "bluer than blue". Light with such short wavelengths
is called "Ultraviolet" light.
How do we know this light exists? One way is that this kind of light causes sunburns. Our skin is
sensitive to this kind of light. If we stay out in this light without sunblock protection, our skin
absorbs this energy. After the energy is absorbed, it can make our skin change color ("tan") or it
can break down the cells and cause other damage.
Energy with wavelengths too long for humans to see
Energy whose wavelength is too long to see is "redder than red". Light with such long
wavelengths is called "Infrared" light. The term "Infra-" means "lower than".
How do we know this kind of light exists? One way is that we can feel energy with these
wavelengths such as when we sit in front of a campfire or when we get close to a stove burner.
Electromagnetic waves travel at the speed of light (29,979,245,800
centimeters per second) and their frequency and wavelength can be
determined by the formulas:
where 'c' is the speed of light in centimeters per second,
the Greek letter lambda λ is the wavelength in centimeters
and the frequency is in cycles per second.
The speed of light is . Calculate the frequency of red light of wavelength 7 x 10-7
Wien's displacement law states that the blackbody curve at any temperature has essentially the same
shape as the curve at any other temperature, except that each wavelength is displaced, or moved over,
on the graph.
T= b/lamda max
where λmax is the peak wavelength in metres, T is the temperature of the blackbody in kelvins
(K), and b is a constant of proportionality called Wien's displacement constant, equal to
The scientific method - body of techniques for investigating phenomena, acquiring new knowledge, or correcting and integrating previous knowledge: observation, hypothesis, experiment, conclusion, reproducibility (someone else can repeat the experiment) Electromagnetic radiation (often abbreviated e-m radiation or emr) is a phenomenon that takes the form of self-propagating waves in a vacuum or in matter. It consists of electric and magnetic field components which oscillate in phase perpendicular to each other and perpendicular to the direction of energy propagation. A small and somewhat variable window of frequencies is sensed by the eyes of various organisms; this is what we call the visible spectrum, or light. Em radiation carries energy and momentum that may be imparted to matter with which it interacts. Wave propagation is any of the ways in which waves travel. The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation.