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Question 31 of 36

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SAT Subject Test

The figure presents 3 energy levels of an atom, represented by 3 parallel horizontal lines. The figure has 2 columns, 1 on either side of the horizontal lines. The column to the left of the lines is labeled n and the column to the right is labeled Energy Above Ground State. The values for n in the left column are 1 for the lowest horizontal line, 2 for the middle line, and 3 for the uppermost line. The values for the energy above ground state are 0 electron-volts for the lowest line, 4 electron-volts for the middle line, and 7 electron-volts for the uppermost line.

Three energy levels of an atom are shown above. Atoms in the n equals 2 state can spontaneously emit photons having which of the following energies?

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4 eV only

Correct Answer: 
Yes

7 eV only

Correct Answer: 
No

3 eV and 4 eV only

Correct Answer: 
No

3 eV and 7 eV only

Correct Answer: 
No

3 eV, 4 eV, 7 eV

Correct Answer: 
No

The correct answer is 4eV only. According to the energy level diagram, atoms in the n equals 2 state have an energy of 4eV above the ground state left parenthesis n equals 1 right parenthesis. Atoms can only emit photons spontaneously when they drop to a lower energy level. According to conservation of energy, the energy of the photon will equal the difference in energy of the two atomic states. For atoms in n equals 2 state, the only lower energy level available is the n equals 1 ground state. So the only photon energy possible is equal to the difference in energy of these two states, 4eV 0 eV, which is equal to 4eV.

Question Difficulty: 
hard