In the operation of a laser
a. stimulated emission occurs.
b. there is a population inversion.
c. the excited state will tend to be metastable.
d. the photons emitted will have transitioned to the ground state.
e. For the answers (a), (b), (c), and (d), three are correct and one is incorrect.
e
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What is the mass of exactly 1 million helium atoms? The atomic mass of helium is 4.00 u.
a. 
b. 
c. 
d. 
The temperature is observed to decrease from
to 
during the evening of a very hot day. What is the relative change in the speed of sound over this time interval?
A. -15% B. -28% C. -1.5% D. -3%
If an electron moves from a higher energy orbital to a lower energy one, the atom will ________.
A. become a different element B. absorb a photon C. become excited D. vibrate E. emit a photon
How many calories are equal to one BTU? (One calorie = 4.186 J, one BTU = 1054 J.)
a. 0.252 c. 252 b. 3.97 d. 397