To increase the current density in a wire of length l and diameter D, you can
a. decrease the potential difference between the two ends of the wire. b. increase the potential difference between the two ends of the wire. c. decrease the magnitude of the electric field in the wire. d. heat the wire to a higher temperature. e. combine both (b) and (d).
B
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How are magnetic fields thought to affect star formation in molecular clouds?
A) They can help resist gravity, so that more total mass is needed before the cloud can collapse to form stars. B) They accelerate the star formation process. C) They allow small stars to form in isolation within gas clouds. D) There are no magnetic fields in interstellar space, so there is no effect.
A 150 W light bulb is designed for an ac voltage of 120 V rms. What is the resistance of the bulb?
A. 150 
B. 144
C. 96.0
D. 68.0
E. 48.0
The first step in cosmic evolution is:
A) particulate evolution. B) stellar evolution. C) chemical evolution. D) biological evolution. E) cultural evolution.
When a 10-kg block is simultaneously pushed toward the east with 20 N and toward the west with 15 N, the combination of these forces on the block is
A) 5 N west. B) 5 N east. C) 35 N east. D) 35 N west.