Why do stars have dark lines in their spectra?
A. They simply don't emit light at certain wavelengths.
B. The cooler atoms in their surface layers absorb the radiation at some wavelengths.
C. Magnetic fields in Earth's atmosphere absorb the radiation at some wavelengths.
D. The statement is false. Stars have bright emission lines in their spectra, but no absorption lines.
Answer: B
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Instructions: On occasion, the notation 
= [A, ?] will be a shorthand notation for 
.
The vector 
has components +5 and +7 along the x and y axes respectively. If the vector is now rotated 90 degrees counterclockwise relative to the original axes, the vector's components are now
A. ?7; ?5.
B. 7; ?5.
C. ?7; 5.
D. 7; 5.
E. 7; 0.
In each element of a series LRC circuit
A) the currents are not in phase. B) the currents and voltages are not in phase. C) the voltages are in phase. D) the currents are in phase. E) the currents and voltages are in phase.
As a space shuttle is launched into orbit, the direction of its acceleration
a. always points upward b. always points downward c. varies between pointing upward and pointing downward d. stays constant
Conduction: Two metal rods, one silver and the other gold, are attached to each other end-to-end. The free end of the silver rod is immersed in a steam chamber at 100°C, and the free end of the gold rod in an ice water bath at 0°C. The rods are both 5.0 cm long and have a square cross-section that is 2.0 cm on a side. No heat is exchanged between the rods and their surroundings, except at the ends. What is the temperature at the point where the two rods are in contact with one another? The thermal conductivity of silver is 417 W/m ? K, and that of gold is 291 W/m ? K.
A. 39°C B. 41°C C. 47°C D. 53°C E. 59°C