Electromagnetic Radiation
Claimed by Carlos Fernandez to edit (Spring 2016) Work on progress by Sungyoung Joo(FALL 2016)
Electromagnetic Radiation
What is a Electromagnetic(EM) Radiation?
Electromagnetic radiation is a form of energy that is all around us and takes many forms, such as radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, and gamma rays.
Before 1873, electricity and magnetism were thought to be two different forces. However, in 1873, Scottish Physicist James Maxwell developed his famous theory of electromagnetism. There are four main electro magnetic interactions according to Maxwell:
- The force of attraction or repulsion between electric charges is inversely proportional to the square of the distance between them
- Magnetic poles come in pairs that attract and repel each other much as electric charges do
- An electric current in a wire produces a magnetic field whose direction depends on the direction of the current
- A moving electric field produces a magnetic field, and vice versa
The four Maxwell's Equations provide a complete description of possible spatial patterns of electric and magnetic field in space.
The Main Idea
If a charge is moved sinusoidally it will emit continuous radiation.
Waves and Fields
As we learned in class, electric field is produced when an electron is accelerating. Likewise, EM radiation is created when an atomic particle, like an electron, is accelerated by an electric field. The movement like this produces oscillating electric and magnetic fields, which travel at right angles to each other in a bundle of light energy called a photon. Photons travel in a harmonic wave at the fastest speed possible in the universe.
Electromagnetic waves are formed when an electric field couples with a magnetic field. Magnetic and electric fields of an electromagnetic wave are perpendicular to each other and to the direction of the wave.
A wavelength (in m) is the distance between two consecutive peaks of a wave. Frequency is the number of waves that form in a given length of time. A wavelength and frequency are interrelated. A short wavelength indicates that the frequency will be higher because one cycle can pass in a shorter amount of time. Likewise, a longer wavelength has a lower frequency because each cycle takes longer to complete.
A Mathematical Model
The position of the particle is defined by a sine wave:
y = ymaxsin(wt)
Where w is the angular frequency.
Amplitude
The Amplitude of the sinusoidal Wave is the height of the peak in the wave measured from the zero line.
Period
The period of the wave is the time between crests.
T = 2pi/w-----(units of seconds)
Frequency
f = 1/T f = w/2pi----(Units Hertz)
Wavelength
The distance between crests in meters. Wavelength is equal to the speed of light times frequency.
ENERGY FLUX
Is defined by the following equation:
S = (1/u0)*(E x B) in W/m^2
where B = E/c
where c = speed of light
History
Electromagnetic radiation of wavelengths in the early 19th century. The discovery of infrared radiation is ascribed to astronomer William Herschel, who published his results in 1800 before the Royal Society of London. Herschel used a glass Triangular prism (optics)|prism to refract light from the Sun and detected invisible rays that caused heating beyond the red part of the spectrum, through an increase in the temperature recorded with a thermometer. These "calorific rays" were later termed infrared.