4. Bats are capable of navigating using the carth's field a plus for an animal that may fly great distances from its roost at night. If, while sleeping during the day, bats are exposed to a field of a similar magnitude but different direction than the earth's field, they are more likely to lose their way during their next lengthy night flight. Suppose you are a researcher doing such an experiment in a location where the carth's field is 50 T at a 60° angle below horizontal. You make a 50-cm-diameter, 100-turn coil around a roosting box; the sleeping bats are at the center of the coil. You wish to pass a current through the coil to produce a field that, when combined with the carth's field, creates a net field with the same strength and dip angle (60° below horizontal) as the carth's field but with a horizontal component that points south rather than north. What are the proper orientation of the coil and the necessary current?
To produce a net magnetic field that has the same strength and dip angle as the Earth's field, but a different direction for the horizontal component, we need to add a magnetic field of the same strength as the Earth's field and with a horizontal component pointing south. We can achieve this by passing a current through the coil in a specific direction.
Let's start by calculating the strength and direction of the magnetic field we need to add. The Earth's magnetic field at the location of the experiment is 50 T at a 60° angle below horizontal. We need to add a magnetic field with the same strength and dip angle, but with a horizontal component pointing south. The horizontal component of the Earth's field is given by B_Earth*cos(60°), which is 25 T. So, we need to add a magnetic field with a strength of 50 T and a horizontal component of -25 T.
To produce this magnetic field, we need to pass a current through the coil. The direction of the current should be such that it produces a magnetic field that adds to the Earth's field in the desired way. We can use the right-hand rule to determine the direction of the current.
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