Electric and magnetic fields are invisible forces that exist wherever electricity is present. An electric field forms around any electrically charged object, while a magnetic field forms around any moving electric charge or current. Together, they shape everything from how your phone receives a signal to how the Earth deflects solar radiation.
How Electric Fields Work
An electric field exists in the space around any electric charge. If you plug a lamp into a wall outlet, an electric field surrounds the cord even when the lamp is switched off, because voltage (the electrical pressure pushing charge through the wire) is still present. The field radiates outward from the charged object and exerts a push or pull on other charged particles nearby.
The strength of an electric field is measured in volts per meter. Higher voltage means a stronger field. Standing near a high-voltage power line, you’re in a much stronger electric field than standing next to a phone charger. Electric fields are relatively easy to block: walls, trees, and even skin significantly reduce their strength.
How Magnetic Fields Work
Magnetic fields appear only when electric charges are moving. Turn that lamp on, and current flows through the cord, generating a magnetic field around it. The same principle operates at the atomic scale, where electrons orbiting inside atoms create the tiny magnetic fields that make permanent magnets possible.
The standard unit for magnetic field strength is the tesla. Because everyday exposures involve very small fields, you’ll more often see values in microtesla (one millionth of a tesla) or in gauss, an older unit where 1 gauss equals 100 microtesla. Unlike electric fields, magnetic fields pass easily through most materials, including walls and human tissue. This is why MRI machines can image deep inside your body and why shielding against magnetic fields is much harder than shielding against electric fields.
The Relationship Between the Two
Electric and magnetic fields are deeply linked. A changing electric field generates a magnetic field, and a changing magnetic field generates an electric field. This back-and-forth relationship, formalized by physicist James Clerk Maxwell in the 1860s, is what makes electromagnetic waves possible. Light, radio signals, microwaves, and X-rays are all self-sustaining ripples of electric and magnetic fields feeding off each other as they travel through space.
At very low frequencies, though, the two fields behave somewhat independently. Near a power line operating at 50 or 60 cycles per second, the electric and magnetic fields don’t radiate away as a wave the way a cell tower signal does. Instead, they stay close to the source and drop off quickly with distance. This is why scientists often discuss electric and magnetic fields separately when talking about household and power-line exposures.
Natural Versus Man-Made Fields
The Earth itself generates a static (constant) magnetic field ranging from about 30 microtesla near the equator to roughly 60 microtesla at the magnetic poles. This geomagnetic field isn’t perfectly steady. It fluctuates with the time of day, the season, and solar activity, sometimes swinging by as much as 1 microtesla within a few minutes during intense solar storms that also produce the Northern Lights.
Man-made fields are a different animal. At power frequencies (50 or 60 Hz, depending on your country), the fields generated by wiring and appliances are alternating, meaning they reverse direction dozens of times per second. In terms of raw strength, man-made power-frequency fields near their sources can be many thousands of times greater than the natural alternating fields produced by the sun or Earth. The critical difference is that man-made field strength drops off rapidly the farther you move from the source.
Fields From Everyday Appliances
Magnetic field levels vary enormously depending on the device and your distance from it. Data from Germany’s Federal Office for Radiation Protection illustrates the pattern clearly:
- Hair dryer: 6 to 2,000 microtesla at 3 cm from the device, but only 0.01 to 7 microtesla at 30 cm, and 0.01 to 0.3 microtesla at 1 meter.
- Microwave oven: 73 to 200 microtesla at 3 cm, dropping to 4 to 8 microtesla at 30 cm, and 0.25 to 0.6 microtesla at 1 meter.
The pattern is consistent across nearly all household appliances: at just 30 cm (about one foot), the magnetic field falls well below the international recommended reference level of 100 microtesla. Distance is the single most effective way to reduce your exposure. Doubling your distance from a small source can cut the field strength by a factor of four or more.
The Electromagnetic Spectrum
Electric and magnetic fields exist across a vast range of frequencies, and the frequency determines how the fields behave and what effects they can have.
At the bottom of the spectrum sit extremely low frequency (ELF) fields, from 0 to 100,000 Hz. Power lines and household wiring operate in this range. Higher up, radiofrequency (RF) fields cover the bands used by AM/FM radio, cell phones, Wi-Fi, and microwave ovens. Higher still, you reach infrared, visible light, and ultraviolet, and eventually X-rays and gamma rays.
Everything below ultraviolet light is classified as non-ionizing radiation, meaning the fields don’t carry enough energy per photon to knock electrons off atoms or break chemical bonds in DNA. X-rays and gamma rays are ionizing and can cause direct molecular damage. This distinction is the foundation of radiation safety guidelines.
How These Fields Interact With Your Body
When non-ionizing fields pass through tissue, the main interaction depends on the frequency. At radio frequencies, the fields cause charged particles and polar molecules (especially water, which makes up most of your body) to oscillate. That oscillation converts electromagnetic energy into kinetic energy, which becomes heat. This is exactly how a microwave oven works: it excites water molecules in food until the friction between them produces enough heat to cook.
At extremely low frequencies, like those from power lines, the primary effect is the induction of weak electric currents inside the body. These induced currents are far smaller than the natural electrical signals your nervous system already uses. At very high exposure levels, strong induced fields could theoretically disrupt cell membranes, but the field strengths required for this are far beyond what you’d encounter in daily life.
The practical takeaway is that for common household and environmental exposures, field strengths drop below recommended limits within a short distance from the source. The fields you encounter walking under a power line or standing next to a running microwave are orders of magnitude weaker than the levels at which measurable biological heating or current induction occurs.