How do astronomers infer the presence of magnetic fields in molecular clouds?
A) by measuring the amount of interstellar reddening
B) by measuring the Doppler shifts of emission lines from gas clumps in the cloud
C) by measuring the infrared light emitted by the cloud
D) by measuring the polarization of starlight passing through the cloud
E) by measuring the amount by which gravity is reduced
D
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Indicate whether the statement is true or false
Three coplanar parallel straight wires carry equal currents I to the right as shown below. Each pair of wires is a distance a apart. The direction of the magnetic force on the middle wire
A. is up out of the plane of the wires. B. is down into the plane of the wires. C. is in the plane of the wires, directed upwards. D. is in the plane of the wires, directed downwards E. cannot be defined, because there is no magnetic force on the middle wire.
Bronco's speed increases after he dives from a hovering helicopter. Relative to an observer in the helicopter Bronco's momentum
A) also increases. B) remains unchanged. C) decreases.
Force on a Wire: The direction of the force on a current-carrying wire in a magnetic field is
A. perpendicular only to the current. B. perpendicular only to the magnetic field. C. perpendicular to both the current and the magnetic field. D. in the direction opposite to the current. E. in same direction as the current.