Hammerhead sharks can detect magnetic fields. In one test sharks trained to get a food
reward when a field was present could unambiguously respond to the field generated by
a current of 1.5 A in a 100 turn coil of wire wrapped around a tank 7.5 m in diameter.
What was the field strength at the center of the tank?
μ0∋ (1.26x10 A )(100)(1.5A)
B = 2r =
B = 2.7 x 10 T = 27 x 10 T = 27 μT
Is this field larger or smaller than the field of the earth?
Earth’s field = 50 μT
A typical MRI solenoid has a length of approximately 1.0 m and a diameter of 1.0 m.
How many turns of wire are required to produce a field of 1.0 T (a typical field) if the
maximum current the wires can carry is 100 A?
B = μ0I L
BL = μ0IN
N = = −6Tm = 8000 turns
μ0I (1.25x10 A )(100 A)