Electromagnetic Force
The electromagnetic force is one of the four fundamental forces. A large part of chemistry, physiology, and molecular biology are regulated by electromagnetic forces. They bind the electrons in an atom to the atomic nucleus, define the three-dimensional structure of proteins, and cause muscles to contract.
The source of the electromagnetic force is electric charge- a fundamental property of matter. Electric charge can either be positive or negative. The smallest unit of electic charge is the charge carried by the electron. The proton carries an equal but opposite positive charge. Because there are two types of charge, positive and negative, the electromagnetic force can be either attractive or repulsive. Opposite charges attract, like charges repel.
<----- (+) (+) ----->
Stationary or static charges generate an electic field. Moving charges produce magnetic fields, and accelerated charges emit electromagnetic radiation, such as visible light or x-rays. It was only in the late 1800's that a theory was put forward unifying electricity, magnetism, and light as different aspects of the electromagnetic force. This was due mainly to the work of James Clerk Maxwell and Micahel Faraday.
The electomagnetic force between the proton and the electron in the
hydrogen atom is 1039 (1,000,000,000,000,000,000,000,000,
000,000,000,000,000) times stronger than the gravitational force
between them. It is directly proportional to the charge on each particle,
and inversely proportional to the square of the distance between them:
Electromagnetic Spectrum
The fundamental particle of the electromagnetic force is the photon. Photons have no mass, and they all travel at exactly the same speed; c, the speed of light. The behavior of photons is somewhat mysterious in that they exhibit both particle and wave properties. In the photoelectric effect, photons act as packets of energy that can knock electrons out of a metal surface. But photons are refracted by water droplets to form a rainbow, and refraction is a property of waves.
Photons are also known as electromagnetic radiation. Electromagnetic radiation has a spectrum of different wavelengths, and each wavelength range has its own designation. The shortest wavelength photons, (those with the highest energy), are called gamma rays. At the long wavelength end, (the lowest energy), are radio waves. Visible light is in the middle.
| Band | Wavelength | Frequency | |
|---|---|---|---|
| MF medium frequency | 300-3000 kHz | ||
| HF high frequency | 3-30 MHz | ||
| Radio | 20 cm - 20 m | 15 MHz - 1.5 GHz | |
| FM | 2.5-3.5 m | 85-120 MHz | |
| ShortWave | 20 cm - 2.5 m | 120 MHz - 1.5 GHz | |
| Microwave | 0.01-20 cm | 1.5-3000 GHz | |
| EHF extremely high frequency | 30-300 GHz | ||
| Far Infrared | 20,000-100,000 nm | 3000-15000 GHz | |
| Near Infrared | 700-20,000 nm | 15000-430,000 GHz | |
| Visible | 400-700 nm | 430,000-750,000 GHz | |
| Red | 620-760 nm | ||
| Orange | 570-620 nm | ||
| Yellow | 550-570 nm | ||
| Green | 470-550 nm | ||
| Blue | 440-470 nm | ||
| Violet | 380-440 nm | ||
| Ultraviolet | 4-400 nm | ||
| Soft XRay | 1-20 nm | ||
| Hard XRay | 0.1-1 nm | ||
| Gamma Ray | |||
The energy of a photon is directly proportional to its frequency , nu , and inversely proportional to its wavelength, lambda. The constant of proportionality, h, is Planck's constant.
Event Horizon
The boundary separating a black hole from the rest of the universe. Beyond this point, nothing can escape being pulled into the black hole. To get past the event horizon, once you are inside, would require that you travel faster than the speed of light.
