What is it about the Sun's corona that astronomers don't understand?
A) No one knows why that part of the Sun's atmosphere does not drift away into space.
B) During total solar eclipses, the corona sometimes disappears from view.
C) The corona seems to absorb 2/3 of the neutrinos that pass through it.
D) The corona is much hotter than layers of the Sun that are closer to the solar interior.
E) The Sun's corona extends to the outer reaches of the solar system.
D
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The red line in the helium spectrum is closer to orange than the red line in the hydrogen spectrum, indicating that it has a higher frequency. Therefore, the photons of red light emitted by helium have __________ energy than those emitted by hydrogen
a. lower b. higher c. the same d. more ionization
An observer stands 3 m from speaker A and 4 m from speaker B. Both speakers, oscillating in phase, produce 170-Hz waves. The speed of sound in air is 340 m/s. What is the phase difference (in radians) between the waves from A and B at the observer's location, point P?
?
?
a.
0
b.
?/2
c.
?
d.
2?
e.
4?
Dallas says that any change in velocity is directly proportional to the time interval over which the change took place. Dana says that is true only when the acceleration is constant. Which one, if either, is correct?
A.
B.
so that ?vx = ?t. C.
always is equal to 
.D.
E.
The total amount of power (in watts, for example) that a star radiates into space is called its ________
A) apparent brightness B) flux C) absolute magnitude D) luminosity