Waves Electric 88 Free Download
Jenell Taitague
E is the electric field vector, and B is the magnetic field vector of the EM wave. For electromagnetic waves E and B are always perpendicular to each other and perpendicular to the direction of propagation. The direction of propagation is the direction of E x B.
When electromagnetic waves travel through a medium, the speed of the waves in the medium is v = c/n(λfree), where n(λfree) is the index of refraction of the medium. The index of refraction n is a properties of the medium, and it depends on the wavelength λfree of the EM wave. If the medium absorbs some of the energytransported by the wave, then n(λfree) isa complex number. For air n is nearly equal to 1 for all wavelengths. When an EM wave travels from one medium with index of refraction n1 into another medium with a different index of refraction n2, then itsfrequency remains the same, but its speed and wavelength change. For air n is nearly equal to 1.
Visible light makes up just a small part of the full electromagnetic spectrum. Electromagnetic waves with shorter wavelengths and higher frequencies include ultraviolet light, X-rays, and gamma rays. Electromagnetic waves with longer wavelengths and lower frequencies include infrared light, microwaves, and radio and television waves.
For a linearly polarized electromagnetic wave traveling in the x-direction, the angle the electric field makes with the y-axis is unique. An unpolarized electromagnetic wave traveling in the x-direction is a superposition of many waves. For each of these waves the electric field vector is perpendicular to the x-axis, but the angle it makes with the y-axis is different for different waves. For unpolarized light traveling in the x-direction Ey and Ez are randomly varying on a timescale that is much shorter than that needed for observation.The diagram on the light depicts unpolarized light. Natural light is, in general, unpolarized.
Electromagnetic waves transportenergy through space. In free space this energy is transported by the wave with speed c. The magnitude of the energy flux S is the amount of energy that crosses a unit area perpendicular to the direction of propagation of the wave per unit time. It is given by
Electromagnetic waves transport energy and momentum across space. The energy and momentum transported by an electromagnetic wave are not continuously distributed over the wave front. Energy and momentum are transported by photons in discrete packages. Photons are the particles of light. Light is "quantized". Photons always move with the speed of light. The energy of each photon is E = hf = hc/λ. The momentum of each photon is E/c = hf/c = h/λ.
Quantum mechanics views photons as quanta or packets of energy. But these quanta behave nothing like macroscopic particles. For a macroscopic particle we assume that we can measure its position and its velocity at any time with arbitrary precision and accuracy. Given that we have done this, we can predict with arbitrary precision and accuracy its subsequent motion. But for any photon, we can only predict the probability that the photon will be found at a given position. That probability can be calculated using the wave equation for electromagnetic waves. Where the wave equation predicts a high light intensity, the probability is large, and where it predicts a low light intensity, the probability is small.
Electric and magnetic fields, also known as electromagnetic fields (EMF), consist of waves of electric and magnetic energy moving together. These energy fields surround us all the time. The World Health Organization, an agency of the United Nations, classifies extremely low frequency electromagnetic fields as possibly carcinogenic to humans based on limited evidence showing an association with childhood leukemia. However, scientific studies have not consistently shown whether exposure to any source of EMF increases cancer risk. Scientists continue to conduct research on the possible health effects of exposure to EMFs in order to improve health risk assessments and protection programs.
Electromagnetic radiation (EMR) consists of waves of electric and magnetic energy moving together through space. An example of electromagnetic radiation is visible light. Electromagnetic radiation can range from low to high frequency, which is measured in hertz, and can range from low to high energy, which is measured in electron volts. Wavelength, another term associated with electromagnetic radiation, is the distance from the peak of one wave to the next.
The waves from power lines and electrical devices have a much lower frequency than other types of EMR, such as microwaves, radio waves or gamma rays. However, a low frequency wave does not necessarily mean that it is low energy; a charging cable for a phone produces a low frequency, low energy electromagnetic field, while a high-tension power line can create a much higher energy electromagnetic field that is still low in frequency.
EMR associated with power lines is a type of low frequency non-ionizing radiation. Electric fields are produced by electric charges, and magnetic fields are produced by the flow of electrical current through wires or electrical devices. Because of this, low frequency EMR is found in close proximity to electrical sources such as power lines. As current moves through a power line, it creates a magnetic field called an electromagnetic field. The strength of the EMF is proportional to the amount of electrical current passing through the power line and decreases as you move farther away. Because of this property, the exposure to an electromagnetic field you would receive from a power line decreases with distance.
Multiple agencies within the federal government regulate EMF. The agency that sets standards for EMF depends on the frequency of the EMF. However, in the United States, there are no federal standards limiting electromagnetic fields from power lines and other similar sources. Some states set standards for the width of right-of-ways under high-voltage transmission lines because of the potential for electric shock.
Electric fields are created by differences in voltage: the higher the voltage, the stronger will be the resultant field. Magnetic fields are created when electric current flows: the greater the current, the stronger the magnetic field. An electric field will exist even when there is no current flowing. If current does flow, the strength of the magnetic field will vary with power consumption but the electric field strength will be constant.
Electromagnetic fields are present everywhere in our environment but are invisible to the human eye. Electric fields are produced by the local build-up of electric charges in the atmosphere associated with thunderstorms. The earth's magnetic field causes a compass needle to orient in a North-South direction and is used by birds and fish for navigation.
One of the main characteristics which defines an electromagnetic field (EMF) is its frequency or its corresponding wavelength. Fields of different frequencies interact with the body in different ways. One can imagine electromagnetic waves as series of very regular waves that travel at an enormous speed, the speed of light. The frequency simply describes the number of oscillations or cycles per second, while the term wavelength describes the distance between one wave and the next. Hence wavelength and frequency are inseparably intertwined: the higher the frequency the shorter the wavelength.
A simple analogy should help to illustrate the concept: Tie a long rope to a door handle and keep hold of the free end. Moving it up and then down slowly will generate a single big wave; more rapid motion will generate a whole series of small waves. The length of the rope remains constant, therefore, the more waves you generate (higher frequency) the smaller will be the distance between them (shorter wavelength).
Exposure to electromagnetic fields is not a new phenomenon. However, during the 20th century, environmental exposure to artificial electromagnetic fields has been steadily increasing as growing electricity demand, ever-advancing technologies and changes in social behaviour have created more and more artificial sources. Everyone is exposed to a complex mix of weak electric and magnetic fields, both at home and at work, from the generation and transmission of electricity, domestic appliances and industrial equipment, to telecommunications and broadcasting.
Tiny electrical currents exist in the human body due to the chemical reactions that occur as part of the normal bodily functions, even in the absence of external electric fields. For example, nerves relay signals by transmitting electric impulses. Most biochemical reactions from digestion to brain activities go along with the rearrangement of charged particles. Even the heart is electrically active - an activity that your doctor can trace with the help of an electrocardiogram.
Low-frequency electric fields influence the human body just as they influence any other material made up of charged particles. When electric fields act on conductive materials, they influence the distribution of electric charges at their surface. They cause current to flow through the body to the ground.
Both electric and magnetic fields induce voltages and currents in the body but even directly beneath a high voltage transmission line, the induced currents are very small compared to thresholds for producing shock and other electrical effects.
Heating is the main biological effect of the electromagnetic fields of radiofrequency fields. In microwave ovens this fact is employed to warm up food. The levels of radiofrequency fields to which people are normally exposed are very much lower than those needed to produce significant heating. The heating effect of radiowaves forms the underlying basis for current guidelines. Scientists are also investigating the possibility that effects below the threshold level for body heating occur as a result of long-term exposure. To date, no adverse health effects from low level, long-term exposure to radiofrequency or power frequency fields have been confirmed, but scientists are actively continuing to research this area.
760c119bf3