How did it happen ?

But although physics governs and shapes matter and movement, picturing how it operates can be tricky — and that's where Dianna Cowern, creator and host of YouTube's "Physics Girl" channel, steps in. Cowern takes a playful approach to physics in her videos, to demonstrate, visualize and enthusiastically explain how it intersects with and influences our lives every day. [Gallery: Dreamy Images Reveal Beauty in Physics]

Cowern first developed an interest in physics in high school, crediting her interest to two teachers who introduced her to "all the cool stuff," Scientific American reported in 2014. After earning a college degree in physics, Cowen produced a lighthearted video called "What to Do With a Physics Degree," and its popularity hinted that producing videos about physics could be both successful and rewarding, Cowern told Scientific American.

The Cause

An electromagnetic field (also EM field) is a physical field produced by electrically charged objects. It affects the behavior of charged objects in the vicinity of the field. The electromagnetic field extends indefinitely throughout space and describes the electromagnetic interaction.

As in the previous opinion, the section is divided into four separate sub-sections based on frequency bands (radio frequency (RF) (100 kHz < f ≤ 300 GHz), intermediate frequency (IF) (300 Hz < f ≤ 100 kHz), extremely low frequency (ELF) (0 < f ≤ 300 Hz), and static (0 Hz) (only static magnetic fields are considered in this opinion). These frequency ranges are discussed in order of decreasing frequency: RF, IF, ELF, and static fields, respectively. For each frequency range the review begins with a description of sources and exposure to the population. This is followed, for each frequency range, by a discussion that is organised according to outcome. For each outcome, relevant human, in vivo, and in vitro data are covered.

There are also frequency bands that are not covered in this opinion since relevant data regarding possible effects on human health are not available or not directly mentioned in the mandate. This includes a part of the radio frequency spectrum which is the lower frequency Terahertz (THz) radiation. Terahertz applications operate between the optical spectrum on the short wavelength side and the radio frequency fields on the longer wavelength side. Applications are mainly imaging and spectroscopy. Other parts of the electromagnetic spectrum that are not discussed include the infrared and ultraviolet frequency bands.

How to make an electromagnetic train, "Physics Girl"-style. Credit: Dianna Cowern / Physics Girl
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