A situation known as "population inversion" is needed for lasing action. What does "population inversion" mean?
A. Electrons are in the -1/2 state.
B. Excited atoms must be at the top of the laser tube.
C. Excited atoms must be at the bottom of the laser tube.
D. The number of excited states that are to emit photons are in greater number than the lower states at which the transition is ending.
E. The number of lower states are in greater number than the upper states participating in the lasing action.
D. The number of excited states that are to emit photons are in greater number than the lower states at which the transition is ending.
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The force of gravity varies with the:
A) product of the two masses. B) inverse of the distance separating the two bodies. C) inverse square of the distance separating the two bodies. D) Both A and B are correct. E) Both A and C are correct.
Substantial heat transfer by conduction can occur over great distances
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