M IGRATION OF BIRDS The migratory pattern of birds is one of the mysteries in the field of biology, and indeed all of science. For example, every winter birds from Siberia fly unerringly to water spots in the Indian subcontinent. There has been a suggestion that electromagnetic induction may provide a clue to these migratory patterns. The earth’s magnetic field has existed throughout evolutionary history.
It would be of great benefit to migratory birds to use this field to determine the direction. As far as we know birds contain no ferromagnetic material. So electromagnetic induction seems to be the only reasonable mechanism to determine direction. Consider the optimal case where the magnetic field B , the velocity of the bird v , and two relevant points of its anatomy separated by a distance l , all three are mutually perpendicular.
From the formula for motional emf, Eq. ( . ), ε = Blv Taking B = × – T, l = cm wide, and v = m/s, we obtain ε = × – × × – × V = × – V = μ V This extremely small potential difference suggests that our hypothesis is of doubtful validity. Certain kinds of fish are able to detect small potential differences.
However, in these fish, special cells have been identified which detect small voltage differences. In birds no such cells have been identified. Thus, the migration patterns of birds continues to remain a mystery. POINTS TO PONDER .
Electricity and magnetism are intimately related. In the early part of the nineteenth century, the experiments of Oersted, Ampere and others established that moving charges (currents) produce a magnetic field. Somewhat later, around , the experiments of Faraday and Henry demonstrated that a moving magnet can induce electric current. .
In a closed circuit, electric currents are induced so as to oppose the changing magnetic flux. It is as per the law of conservation of energy. However, in case of an open circuit, an emf is induced across its ends. How is it