justin loves to make electromagnets in his spare time. he wanted to teach his friend jimmy about what the iron core of an electromagnet does. what is the best explanation?
a) it is a conductor that allows more current to flow through the electromagnet.
b) it produces a magnetic field that adds to the overall magnetic field of the electromagnet.
c) it is an insulator that protects people from getting shocked.
d) it produces a current that passes through the coil.

Certain bacteria (such as aquaspirillum magnetotacticum) tend to swim toward the earth’s geographic north pole because they contain tiny particles, called magnetosomes, that are sensitive to a magnetic field. if a transmission line carrying 100 a is laid underwater, at what range of distances would the magnetic field from this line be great enough to interfere with the migration of these bacteria? (assume that a field less than 5% of the earth’s field would have little effect on the bacteria. take the earth’s field to be 5.0 * 10-5 t, and ignore the effects of the seawater.)