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Transcript
Electromagnetic radiation – the nature of light
Rearranged from Wikipedia
Electromagnetic radiation (sometimes abbreviated EMR) takes the form of self-propagating
waves in a vacuum or in matter. EM radiation has an electric and magnetic field component which
oscillate in phase perpendicular to each other and to the direction of energy propagation.
The speed of light is 299,792,458 m/s about 3×108 m/s independent of its colour = frequency.
An important aspect of the nature of light is its frequency. The frequency of a wave is its rate of
oscillation and is measured in hertz, the SI unit of frequency, where one hertz is equal to one
oscillation per second. Light usually has a spectrum of frequencies which sum together to form the
resultant wave.
A wave consists of successive troughs (=Mulde) and crests (=Gipfel), and the distance between two
adjacent crests or troughs is called the wavelength. Waves of the electromagnetic spectrum vary in
size, from very long radio waves the size of buildings to very short gamma rays smaller than atom
nuclei. Frequency is inversely proportional to wavelength, according to the equation:
where v is the speed of the wave (c in a vacuum, or less in other media), f is the frequency and λ is
the wavelength. Waves with higher frequencies have shorter wavelengths. Lower frequencies have
longer wavelengths, assuming the speed of the wave is the same.[1]The energy in electromagnetic
waves is sometimes called radiant energy.
The higher the frequency of a wave, the higher is its energy.
The Electromagnetic spectrum
Electromagnetic radiation is classified into types according to the frequency of the wave, these
types include (in order of increasing frequency): radio waves, microwaves, terahertz radiation,
infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays. Of these, radio waves
have the longest wavelengths and Gamma rays have the shortest. Only a small window of
frequencies, called visible spectrum or light, is sensed by the eye of various organisms, with
variations of the limits of this narrow spectrum.
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White light can be separated into different frequency waves (for example by a prism).
Visible light
This is the range in which the sun and stars similar to it emit most of their radiation. It is probably
not a coincidence that the human eye is sensitive to the wavelengths that the sun emits most
strongly. Visible light (and near-infrared light) is typically absorbed and emitted by electrons in
molecules and atoms that move from one energy level to another. The light we see with our eyes is
really a very small portion of the electromagnetic spectrum. A rainbow shows the optical (visible)
part of the electromagnetic spectrum; infrared (if you could see it) would be located just beyond the
red side of the rainbow with ultraviolet appearing just beyond the violet.
EM radiation with a wavelength between 380 nm and 760 nm is detected by the human eye and
perceived as visible light. Other wavelengths, especially near infrared (longer than 760 nm) and
ultraviolet (shorter than 380 nm) are also sometimes referred to as light, especially when the
visibility to humans is not relevant.
Experiment: Diffraction of white light on a fine grid