Since the rest energy of an electron and its antiparticle a positron is 0.511 MeV, a gamma ray must have an energy larger than 1.022 MeV to produce an electron-positron pair
a. True
b. False
Indicate whether the statement is true or false
True
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Potassium Iodide (chemical formula: KI) has a face-centered cubic structure (just like sodium chloride). If the distance between crystal planes is d = 0.353 nm and X-rays of wavelength ? = 0.0934 nm are used, what is the smallest angle ? at which a diffraction maximum may be obtained?
A. 9.92° B. 7.60° C. 13.3° D. 15.5° E. 6.52°
What is the zone of avoidance?
A. a part of the sky in which astronomers cannot observe due to bright emission from interstellar dust B. a quadrant of the Galaxy where no galaxies exist C. a part of the region of the Solar System where it is too dangerous to send spacecraft D. the region of the sky where no galaxies are seen due to obscuring dust in the Milky Way
When a jet plane exceeds the speed of sound, a(n) ______________ forms, resulting in a sonic boom
Fill in the blank(s) with correct word
Why are auroras produced only near the northern and southern magnetic poles of a planet?
a. Those are the locations where the atmosphere is thinner, letting particles penetrate. b. The poles are pointing toward the Sun, so they receive more solar wind particles. c. The oxygen atoms responsible for auroral emission only exist near the poles. d. Charged particles are forced to flow along Earth's magnetic field lines, which come out of Earth's poles.