When a current flows through a metal wire, the moving charges are
A) only electrons.
B) negative metal ions.
C) only protons.
D) positive metal ions.
E) both protons and electrons.
A
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In an energy level transition from the n = 2 state to the n = 1 state for a hydrogen atom a photon will be ___________
Fill in the blank(s) with correct word
The two photons produced in an electron-positron annihilation have equal but oppositely-directed momenta to match the zero momentum of the electron-positron pair. Which of the following conservation laws are obeyed in the pictured interaction?
a. Conservation of energy. b. Conservation of momentum. c. Conservation of charge. d. Both a. and b. but not c. e. All of a., b. and c.
The photons coming from an excited gas create a(n) ____ spectrum
a. absorption b. emission c. continuous d. Doppler e. ionization
What is the galactic fountain model?
A) a model in which interstellar water vapor can condense to form liquid water rain drops falling toward the galactic disk B) a model that assumes the Milky Way is a spiral galaxy and looks like a whirlpool from above C) a model in which jets of hot, ionized gas blow out of the galactic center and leave the galaxy forever D) a model in which superbubbles blow hot, ionized gas out of the galactic disk and into the halo, where the gas cools down and falls back into the disk