An electric current can consist of
a. positive ions flowing in a liquid c. electrons flowing in a wire
b. negative ions flowing in a liquid d. all of the above
D
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Substance A has twice the specific “heat” as substance B. Suppose we put 100-g blocks of these substances in direct sunlight. Assume both blocks are black and present the same surface area to the incoming sunlight. After a certain period of time, how are the temperature changes ?TA and ?TB of these blocks related (assuming they lose little heat to their surroundings)?
A. ?TA ? 2?TB B. ?TA ? ?TB, as both receive the same amount of energy C. ?TB ? 2 ?TA D. ?TA = ?TB = 0, because neither receives any heat
Two solenoids are each made of 2000 turns of copper wire per meter. Solenoid I is 2 m long, while solenoid II is 1 m long. When equal currents are present in the two solenoids, the ratio of the magnetic field BI along the axis of solenoid I to the magnetic field BII along the axis of solenoid II, BI/BII, is
A. 1/4. B. 1/2. C. 1. D. 2 E. 4.
A long, vertical, metallic wire carries downward electric current. What is the direction of the magnetic field it creates at a point 2 cm horizontally east of the center of the wire?
1.north 2.south 3.east 4.west 5.up
About 74% by mass of Earth's crust is composed of the two elements
a. oxygen and iron. b. aluminum and iron. c. oxygen and silicon. d. silicon and aluminum.