It is known that birds can detect the earth's magnetic field,but the mechanism of how they do this is not known.It has been suggested that perhaps they detect a motional emf as they fly north to south,but it turns out that the induced voltages are small compared to the voltages normally encountered in cells,so this is probably not the mechanism involved.To check this out,calculate the induced voltage across the wingtips of a wild goose with a wingspan of $1.2 \mathrm {~m}$ if it is flying directly south at $13 \mathrm {~m} / \mathrm { s }$ at a point where the earth's $\vec { B }$ field is 5.0 ×10^-5 T directed downward from the horizontal by $40 ^ { \circ }$ A)0.50 mV B)0.60 mV C)0.78 mV D)0.060 mV E)0.25 mV

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Quizplus · Accepted Answer

The induced voltage is given by:$$emf=Blv\sin\theta$$where:* $B$ is the magnetic field strength* $l$ is the length of the conductor* $v$ is the velocity of the conductor* $\theta$ is the angle between the magnetic field and the velocity vectorIn this case, the length of the conductor is the wingspan of the goose, the velocity is the speed of the goose, and the magnetic field strength is 5.0 ×10^-5 T. The angle between the magnetic field and the velocity vector is 40°.Plugging these values into the equation, we get:$$emf=(5.0\times10^{-5}\text{ T})(1.2\text{ m})(13\text{ m/s})\sin40^\circ=0.50\text{ mV}$$Therefore, the induced voltage across the wingtips of the goose is 0.50 mV.

It Is Known That Birds Can Detect the Earth's Magnetic 1.2 m1.2 \mathrm {~m}1.2 m

It Is Known That Birds Can Detect the Earth's Magnetic $1.2 \mathrm {~m}$