A police officer parked at the curb turns on his lights and siren, waits for traffic to clear, then pulls out and heads down the street. For an observer down the street, which is true? A. The frequency of the siren is higher and the wavelength is shorter than it was at first.
B. The wavelength of the siren is shorter than it was at first, but the frequency is the same.
C. The wavelength of the siren is shorter and the frequency is lower than it was at first.
D. The frequency of the siren is higher than it was at first, but the wavelength is the same.

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.)