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6 Electric and Magnetic Fields in Life
• Electric field of a heart defibrillator: 300–500 V/m, producing a 700 mA in pulse
lasting 30 ms, delivering about 100 J to the tissue.
• Equatorial magnetic field of Earth at surface: About half a gauss.
• Magnetic fields near power lines: A few tens of milligauss.
• Magnetic field near appliances with motors: Several hundred milligauss.
• Magnetic field next to strong ‘refrigerator magnet’ or speaker magnet: About
2000–10,000 gauss (1 T).
• Magnetic field of an MRI scanner: About 5000–30,000 gauss.
6.5.5 Biogenerated Strong Electric Fields
Some life forms have developed the ability to create large enough electric fields and
currents to stun their prey. Eels can produce up to 600 V across their bodies using
a series of specialized muscle cells. Other ‘weak electric fish’ make electric pulses
or electric field waves around themselves so that any other object, or another fish,
can be detected with special skin organs by the disturbance of the electric field they
produce. Sharks also have this capability.
6.5.6 Biodetection of Electric Fields
Sharks have sensitive bioelectric sensors giving them ‘electroreception’, used for
location relative to other nearby sharks or fish, and for detecting nearby objects.
The shark generates a surrounding external electric field from its head to its tail
using an electric organ within its body near its tail. The field can be individually
tailored for shark-to-shark identification. The bioelectric sensors are found on the
skin of the head. Objects nearby with a different electric impedance than sea water
will affect the field. Significant changes within a body length are detectable by the
head sensors.
Electroreception has also been found in some fish and in bees.
Sadly, we humans do not seem to have any biosensors for electric fields until the
field becomes strong enough to do damage.
6.5.7 Biodetection of Magnetic Fields
There is evidence that pigeons, turtles, worms, and some bees have magnetic field
sensors to orient themselves in the Earth’s magnetic field. The magnetic particles,
nanosize magnetite (FeO·Fe 2 O 3 ) crystals, in the nerve tissue of the nasal cavity of
homing pigeons, respond to external fields by rotating.
6 Electric and Magnetic Fields in Life
• Electric field of a heart defibrillator: 300–500 V/m, producing a 700 mA in pulse
lasting 30 ms, delivering about 100 J to the tissue.
• Equatorial magnetic field of Earth at surface: About half a gauss.
• Magnetic fields near power lines: A few tens of milligauss.
• Magnetic field near appliances with motors: Several hundred milligauss.
• Magnetic field next to strong ‘refrigerator magnet’ or speaker magnet: About
2000–10,000 gauss (1 T).
• Magnetic field of an MRI scanner: About 5000–30,000 gauss.
6.5.5 Biogenerated Strong Electric Fields
Some life forms have developed the ability to create large enough electric fields and
currents to stun their prey. Eels can produce up to 600 V across their bodies using
a series of specialized muscle cells. Other ‘weak electric fish’ make electric pulses
or electric field waves around themselves so that any other object, or another fish,
can be detected with special skin organs by the disturbance of the electric field they
produce. Sharks also have this capability.
6.5.6 Biodetection of Electric Fields
Sharks have sensitive bioelectric sensors giving them ‘electroreception’, used for
location relative to other nearby sharks or fish, and for detecting nearby objects.
The shark generates a surrounding external electric field from its head to its tail
using an electric organ within its body near its tail. The field can be individually
tailored for shark-to-shark identification. The bioelectric sensors are found on the
skin of the head. Objects nearby with a different electric impedance than sea water
will affect the field. Significant changes within a body length are detectable by the
head sensors.
Electroreception has also been found in some fish and in bees.
Sadly, we humans do not seem to have any biosensors for electric fields until the
field becomes strong enough to do damage.
6.5.7 Biodetection of Magnetic Fields
There is evidence that pigeons, turtles, worms, and some bees have magnetic field
sensors to orient themselves in the Earth’s magnetic field. The magnetic particles,
nanosize magnetite (FeO·Fe 2 O 3 ) crystals, in the nerve tissue of the nasal cavity of
homing pigeons, respond to external fields by rotating.