electromagnetic field
Meaning of electromagnetic field: The invisible region of electric and magnetic force around anything carrying current, from a power line to a phone.
Definition of electromagnetic field
An electromagnetic field is the region of electric and magnetic force surrounding a charged object or a flow of electric current. Every device that uses electricity produces one. Fields are described by their frequency, and frequency decides what they can do to matter: only the highest frequencies carry enough energy to break chemical bonds.
What is the important division?
| Type | Examples | Can it break chemical bonds? |
|---|---|---|
| Ionizing | X-rays and gamma rays | Yes, and it can damage DNA directly |
| Non-ionizing, high frequency | Microwaves, radio and mobile phone signals | No, though it can heat tissue |
| Non-ionizing, low frequency | Power lines, household wiring and appliances | No, though it induces weak currents in tissue |
This division does more work than any other idea in the subject, and it is why the general word radiation covers such different things.
What effects are established?
At sufficient intensity, high frequency fields heat tissue, which is how a microwave oven works and what the international exposure limits are set to prevent. Very strong low frequency fields can stimulate nerve and muscle directly. Fields at close range can interfere with implanted devices such as pacemakers and defibrillators, which is why those carry advice about specific equipment. Magnetic resonance imaging uses an extremely strong static magnetic field, and the danger there is mechanical: loose metal objects become projectiles, which is why the scan room is controlled.
What about cancer?
This has been studied for decades, first around power lines and later around mobile phones. Large population studies have not established that everyday exposure to non-ionizing fields causes cancer. International review bodies have placed both low frequency magnetic fields and radiofrequency fields in a category meaning a link cannot be entirely excluded on current evidence, which reflects residual uncertainty rather than demonstrated harm. The contrast with electromagnetic radiation at ionizing frequencies is stark, since there the cancer risk is established and dose-related.
What is the field around an appliance actually like?
Strength falls off steeply with distance. The magnetic field close to a running motor or a charger is far higher than the field a short step away, so exposure from an appliance across a room is a small fraction of the exposure from holding it. The same geometry applies to power lines, where measured field strength at ground level drops quickly as one moves to the side.
Are there rules for exposure?
International bodies publish limits for occupational and public exposure, set well below the levels at which heating or nerve stimulation begins, and national rules for equipment and transmitters are written against them.
Also known as
Used in a sentence
The implant card noted that strong electromagnetic fields could interfere with the device.
Good to know
The distinction that matters is ionizing against non-ionizing: x-rays carry enough energy to damage DNA directly, while power line and radiofrequency fields do not, whatever their strength.
Word origin
Where “electromagnetic field” comes from
Electric traces to the Greek elektron, meaning amber, which attracts light objects when rubbed; magnet comes from Magnesia, the district where lodestone was found.