Electromagnetic Fields
After reading this section you will be able to do the following:
Describe the magnetic fields that surround a current carrying conductor.
Iron filings scattered in the vacinity of a current carrying wire will reveal a magnetic field perpendicular to the current flow. Magnetic field lines directed out of the page towards the reader is signified by a dot (like the point of an arrow). Magnetic field lines directed into the page, away from the reader, are signified as an x (like the back of an arrow).
Magnets are not the only source of magnetic fields. In 1820, Hans Christian Oersted discovered that an electric current flowing through a wire caused a nearby compass to deflect. This indicated that the current in the wire was generating a magnetic field. Oersted studied the nature of the magnetic field around the long straight wire. He found that the magnetic field existed in circular form around the wire and that the intensity of the field was directly proportional to the amount of current carried by the wire. He also found that the strength of the field was strongest next to the wire and diminished with distance from the conductor until it could no longer be detected. In most conductors, the magnetic field exists only as long as the current is flowing (i.e. an electrical charge is in motion). However, in ferromagnetic materials the electric current will cause some or all of the magnetic domains to align and a residual magnetic field will remain.
Using the right-hand-rule will help determine the direction of the magnetic field induced by a current.Oersted also noticed that the direction of the magnetic field was dependent on the direction of the electrical current
in the wire. A three-dimensional representation of the magnetic field is shown below. There is a simple rule for remembering the direction of the magnetic field around a conductor. It is called the right-hand rule. If a person grasps a conductor in one’s right hand with the thumb pointing in the direction of the current, the fingers will circle the conductor in the direction of the magnetic field.
Electromagnetic Fields
Caution about the Right-Hand Rule
For the right-hand rule to work, one important thing that must be remembered about the direction of current flow. Standard convention has current flowing from the positive terminal to the negative terminal. This convention is credited to Benjamin Franklin who theorized that electric current was due to a positive charge moving from the positive terminal to the negative terminal. However, it was later discovered that it is the movement of the negatively charged electron that is responsible for electrical current
. Rather than changing several centuries of theory and equations, Franklin’s convention is still used today.
Electromagnetic fields (EMFs) are a form of energy that is present in the natural environment as well as being generated by human-made sources. They consist of electric and magnetic fields that oscillate at various frequencies. EMFs are produced by a wide range of sources, including power lines, electrical appliances, wireless devices, and natural phenomena such as lightning.
**EMFs can be categorized into two main types: ionizing and non-ionizing radiation. Ionizing radiation has enough energy to remove tightly bound electrons from atoms, leading to the formation of charged particles or ions. Examples of ionizing radiation include X-rays and gamma rays, which are commonly used in medical imaging and radiation therapy. Non-ionizing radiation, on the other hand, does not have enough energy to remove electrons from atoms but can still interact with living tissue.**
The potential health effects of exposure to EMFs have been a subject of scientific research and public concern for several decades. The most well-known health effect associated with EMF exposure is the increased risk of cancer. However, the scientific consensus based on extensive research is that there is no conclusive evidence linking EMF exposure from everyday sources to adverse health effects.
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