Electric fish navigate by responding to changes in the current in seawater. This current is due to a potential difference of around 3.0 V generated by the fish and is about 14 mA within a centimeter or so from the fish. Receptor cells in the fish are sensitive to the current. Since the current is at some distance from the fish, the sensitivity of these cells suggests that they might be responding to the magnetic field created by the current. To get some estimate of how sensitive the cells are, we can model the current as that of a long, straight wire with the receptor cells 2.20 cm away. What is the strength of the magnetic field at the receptor cells?

Explanation:

current I = 14 x 10⁻³ A

distance of current d =  2.2 x 10⁻² m

Magnetic field B due to a long straight current carrying wire

B = (μ₀ /4π) x (2 I / d )

= 10⁻⁷ x 2 x 14 x 10⁻³ / 2.2 x 10⁻²

= 12.72 x 10⁻⁸ T .

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the total distance traveled by the car is

30km + 49km = 79 km .