MCAT Physics Question 125: Answer and Explanation
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Question: 125
5. The figure below illustrates an electron with initial energy of –10 eV moving from point A to point B. What change accompanies the movement of the electron?
- A. Absorption of a photon
- B. Emission of a photon
- C. Decrease in the atom's work function
- D. Increase in the atom's total energy
Correct Answer: B
Explanation:
The electron moves from a higher energy level to a lower energy level; this can only occur if the extra energy is dissipated through the emission of a photon. If the electron moved from B to A, it would absorb a photon and increase the atom's total energy; however, the opposite is occurring, so choices (A) and (D) can be eliminated. The work function is the amount of energy required to eject an electron from a material; when moving from A to B, the electrical potential energy of the atom decreases, meaning that more energy will be required to free the electron from the atom, eliminating choice (C).