AP Physics 2 Quiz: Emission And Absorption Spectra

What this quiz covers

This quiz focuses on Emission And Absorption Spectra, giving you a quick way to practice the rules, question types, and explanations that matter most for AP Physics 2.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

Question 1

1. any value, because electron energy levels form a continuum in a gas.
2. the energy the electron emits while it is being raised to a higher level.
3. a value set mainly by the intensity of the incident light rather than level spacing.
4. the difference between two allowed quantized energy levels of the atom. (correct answer)

Explanation: This question tests understanding of emission and absorption spectra. In atoms, electrons occupy quantized energy levels and can only transition between these discrete states. For an electron to move from a lower to a higher energy level, it must absorb a photon whose energy exactly equals the difference between those two levels. If the photon energy doesn't match any allowed transition, it cannot be absorbed and passes through the gas. Choice C incorrectly suggests electrons emit energy while being raised to higher levels, which violates energy conservation. Remember that absorption requires photon energies to exactly match allowed energy-level differences.

Question 2

1. An electron absorbed that photon to jump to a higher quantized energy level. (correct answer)
2. An electron emitted that photon while absorbing energy and dropping to a lower level.
3. An electron absorbed that photon because it can take any energy in a continuous band.
4. The photon was removed because the beam intensity sets which wavelengths can propagate.

Explanation: This question tests understanding of emission and absorption spectra. When a photon at 540 nm is missing from the spectrum after passing through gas, it means an atom absorbed that photon. The absorption occurred because the photon's energy exactly matched the energy difference needed to promote an electron from a lower to a higher quantized energy level. Choice B incorrectly describes emission (photon release) rather than absorption and suggests electrons drop to lower levels during absorption, which is backwards. The key principle is that missing photons in absorption spectra indicate upward electron transitions between quantized levels.

Question 3

1. It equals the energy difference between the initial and final quantized levels. (correct answer)
2. It equals the average energy of all possible electron energies in the atom.
3. It is determined by the brightness of the light source, not by level spacing.
4. It is released by the electron during absorption as it falls to a lower level.

Explanation: This question tests understanding of emission and absorption spectra. When an atom absorbs a photon, the photon's energy must exactly match the energy difference between the electron's initial level and a higher allowed level. This energy conservation ensures that the electron gains precisely the right amount of energy to make the quantum jump. Choice D incorrectly suggests energy is released during absorption and that electrons fall to lower levels, which describes emission rather than absorption. The fundamental principle is that absorbed photon energy equals the energy gap between quantized levels in upward transitions.

Question 4

1. The electron transitions to a higher allowed energy level because the photon energy matches the level separation. (correct answer)
2. The electron transitions to a lower allowed energy level because absorbing a photon releases energy.
3. The electron transitions to any energy value because atomic levels are continuous at low pressure.
4. The electron remains in place, and the line appears because intensity determines which wavelengths can propagate.

Explanation: This question tests understanding of emission and absorption spectra. During the absorption step, an atom absorbs a photon whose energy exactly matches the energy difference between two allowed energy levels. This absorbed energy promotes an electron from a lower energy level to a higher energy level, conserving energy in the process. The electron cannot transition to arbitrary energies because atomic energy levels are quantized. Later, the electron may spontaneously drop back down, emitting a photon of the same energy, though possibly in a different direction. Choice B incorrectly claims absorption causes the electron to move to a lower level, which would violate energy conservation. The key insight is that absorption always involves electrons gaining energy and moving to higher allowed levels.

Question 5

1. It moves to a higher allowed energy level by absorbing a photon whose energy matches the level difference. (correct answer)
2. It moves to a lower allowed energy level by absorbing a photon and emitting the energy difference.
3. It can move to any energy because energy levels are continuous, so absorption removes random wavelengths.
4. It stays in the same level, and the missing wavelengths occur because intensity sets the allowed transitions.

Explanation: This question tests understanding of emission and absorption spectra. When light passes through a cool gas, atoms can absorb photons whose energies exactly match the energy difference between two allowed energy levels. During absorption, an electron gains energy equal to the photon's energy and transitions from a lower energy level to a higher energy level. This removes specific wavelengths from the transmitted light, creating dark absorption lines. The electron cannot move to arbitrary energies because atomic energy levels are quantized, not continuous. Choice B incorrectly states the electron moves to a lower level during absorption, which would violate energy conservation. The strategy is to remember that absorption always involves electrons moving up in energy by gaining photon energy.

Question 6

1. Only certain photon energies are emitted because atoms have continuous energy bands but emit intermittently.
2. Only certain photon energies are emitted because electrons release photons when transitioning between quantized levels. (correct answer)
3. Only certain photon energies are emitted because electrons must absorb photons before emitting them at the same energy.
4. Only certain photon energies are emitted because line spacing is determined by the brightness of the hot gas.

Explanation: This question tests understanding of emission and absorption spectra. In a hot gas, electrons are excited to higher energy levels through thermal collisions. These excited electrons spontaneously transition back to lower energy levels, emitting photons whose energies equal the difference between the initial and final quantized energy levels. Since atoms have discrete energy levels rather than continuous bands, only specific energy differences (and thus specific photon energies) are possible. This produces the characteristic bright emission lines at specific wavelengths. Choice C incorrectly suggests electrons must first absorb photons before emitting them, confusing emission with fluorescence. The key principle is that emission spectra reveal the quantized nature of atomic energy levels through discrete photon energies.

Question 7

1. They occur because electron energies in the atom are continuous, producing all wavelengths but only some are detected.
2. They occur because electrons emit photons only when dropping between allowed energy levels, giving specific energies. (correct answer)
3. They occur because electrons must emit energy when absorbing photons, so only certain colors appear.
4. They occur because the spacing of lines is set by the light intensity from the discharge, not energy levels.

Explanation: This question tests understanding of emission and absorption spectra. When electrons in hydrogen atoms are excited by the electric discharge, they jump to higher energy levels. These excited electrons then spontaneously drop back down to lower energy levels, emitting photons with energies exactly equal to the difference between the initial and final energy levels. Since atoms have quantized (discrete) energy levels rather than continuous ones, only specific energy transitions are possible, producing photons of specific wavelengths that appear as discrete bright lines. Choice A incorrectly suggests energy levels are continuous, which would produce a continuous spectrum rather than discrete lines. The key strategy is to remember that discrete spectral lines always indicate quantized energy levels with specific allowed transitions.

Question 8

1. electrons absorb only photons matching allowed energy-level gaps, promoting them to higher levels. (correct answer)
2. electrons emit photons at all energies, removing yellow light from the beam.
3. electrons have continuous energies, so they absorb a narrow band by resonance.
4. line position is determined by how bright the source is, not by energy levels.

Explanation: This question tests understanding of emission and absorption spectra. When white light passes through cool sodium vapor, sodium atoms absorb photons whose energies exactly match the energy differences between quantized levels. These absorbed photons promote electrons from lower to higher energy levels, removing those specific wavelengths from the transmitted light and creating dark absorption lines. Choice B incorrectly suggests electrons emit photons during absorption, which reverses the actual process where absorption involves electrons gaining energy and moving up. The fundamental principle is that absorption lines occur when photons matching allowed energy transitions are removed from continuous light.

Question 9

1. light intensities, which set the allowed wavelengths emitted by each gas.
2. quantized energy-level spacings, so the photon energies from transitions differ by element. (correct answer)
3. continuous energy-level distributions, producing different interference patterns.
4. rates of absorbing photons while emitting energy, which selects element-specific wavelengths.

Explanation: This question tests understanding of emission and absorption spectra. Different elements have different nuclear charges and electron configurations, resulting in unique sets of quantized energy levels with different spacings. When electrons transition between these levels, they emit photons with energies equal to the level differences, which vary by element. This creates a unique spectral fingerprint for each element, allowing identification through spectroscopy. Choice D incorrectly suggests the process involves absorbing photons while emitting energy, which confuses the emission mechanism. Remember that each element's unique energy-level structure produces its characteristic spectral lines.

Question 10

1. absorb photons whose energies match allowed electron transitions between quantized energy levels. (correct answer)
2. absorb more strongly at wavelengths where the light source intensity is lowest.
3. absorb photons of any energy, but only certain wavelengths are removed by collisions.
4. emit photons while absorbing them, canceling most colors except a few wavelengths.

Explanation: This question tests understanding of emission and absorption spectra. When white light passes through cool sodium vapor, atoms absorb photons whose energies exactly match the energy differences between their quantized electron energy levels. This absorption removes specific wavelengths from the continuous spectrum, creating dark lines at those wavelengths. The absorbed energy promotes electrons from lower to higher energy levels. Choice B incorrectly suggests atoms can absorb photons of any energy, which would create a continuous absorption rather than discrete lines. Remember that absorption lines occur at wavelengths corresponding to allowed electron transitions between quantized energy levels.

Question 11

1. The atoms emit photons only when electrons drop between specific energy levels, so only certain photon energies occur. (correct answer)
2. The spacing of the lines is determined mainly by the intensity of the discharge current in the tube.
3. The electrons emit energy when they absorb photons, producing only a few allowed colors.
4. The atoms have continuous energy levels, so the spectrum should appear as separated bands instead of a rainbow.

Explanation: This question tests understanding of emission and absorption spectra. In hydrogen atoms, electrons occupy specific quantized energy levels, not continuous ones. When electrons drop from higher to lower energy levels, they emit photons with energies exactly equal to the difference between those levels. Since only certain energy differences are possible, only specific photon energies (and thus specific colors) appear as discrete lines. Choice B incorrectly claims continuous energy levels, which would produce a continuous spectrum, not discrete lines. The key strategy is: discrete spectral lines always indicate quantized energy levels with specific allowed transitions.

Question 12

1. Electrons emit photons while absorbing them, so the missing colors correspond to emitted energies.
2. Atoms absorb only photons that match energy-level gaps, exciting electrons to higher allowed energy levels. (correct answer)
3. Atoms absorb photons of all energies, but re-emit only two colors, leaving two dark lines.
4. Energy levels are continuous, but the detector resolves only two wavelengths because the light is dim.

Explanation: This question tests understanding of emission and absorption spectra. When white light passes through cool sodium vapor, sodium atoms absorb only those photons whose energies exactly match the energy differences between their quantized levels. These absorbed photons excite electrons from lower to higher energy levels, removing those specific wavelengths from the transmitted light and creating dark absorption lines. The two dark lines correspond to two specific allowed transitions in sodium atoms. Choice B incorrectly suggests atoms absorb all energies but re-emit only two, which violates energy conservation and quantization. The strategy is: absorption lines occur at the same wavelengths as emission lines because they involve the same energy-level transitions.

Question 13

1. Different gases emit photons when absorbing them, so the observed lines depend mainly on the input light intensity.
2. Different gases have the same energy levels, but their line spacing changes because their brightness differs.
3. Different gases have continuous energy levels, so random collisions select different wavelengths each time.
4. Different gases have different quantized energy-level spacings, so their allowed transition photon energies differ. (correct answer)

Explanation: This question tests understanding of emission and absorption spectra. Each element has a unique set of quantized energy levels determined by its nuclear charge and electron configuration. Different gases therefore have different energy-level spacings, leading to different sets of allowed transitions and thus different emission line patterns. This uniqueness allows spectroscopy to identify elements. Choice D incorrectly claims all gases have the same energy levels, which would make spectroscopic identification impossible. The key concept is: each element's unique energy-level structure produces a characteristic spectral fingerprint.

Question 14

1. continuous electron energies, so any wavelength can be absorbed or emitted but only some are detected.
2. electrons emitting photons while absorbing them, producing identical missing and bright lines.
3. line positions controlled primarily by the intensity of the light source and the gas density.
4. the same quantized energy differences between atomic levels, matching photon energies in either direction. (correct answer)

Explanation: This question tests understanding of emission and absorption spectra. Both emission and absorption involve the same quantized energy levels within atoms. In absorption, electrons jump from lower to higher levels by absorbing photons with energies matching the level difference. In emission, electrons fall from higher to lower levels, emitting photons with the same energy differences. Since the energy gaps between levels are fixed, the wavelengths for absorption and emission are identical. Choice C incorrectly suggests electrons emit while absorbing, which is physically impossible. The key insight is that spectral lines correspond to specific energy differences, regardless of transition direction.

Question 15

1. Electrons emit energy while absorbing photons, producing a few preferred wavelengths.
2. The spacing of spectral lines is determined by the intensity of the discharge current.
3. Electrons in atoms have quantized energy levels, so photons are emitted only for specific energy differences. (correct answer)
4. Electrons can have any energy, so emitted photons form lines set by the tube's temperature.

Explanation: This question tests understanding of emission and absorption spectra. In hydrogen gas, electrons occupy quantized energy levels, meaning they can only exist at specific, discrete energy values. When electrons transition from higher to lower energy levels, they emit photons with energies exactly equal to the difference between those levels, producing light at specific wavelengths only. Choice B incorrectly suggests electrons can have any energy, which would produce a continuous spectrum rather than discrete lines. The key strategy is to remember that spectral lines correspond to specific energy differences between quantized atomic energy levels.

Question 16

1. energy levels that vary continuously, so only certain wavelengths survive interference.
2. quantized electron energy levels, so emitted photons correspond to specific transitions. (correct answer)
3. electrons that emit energy when absorbing photons, producing discrete missing colors.
4. line positions determined mainly by the intensity of the electric field in the tube.

Explanation: This question tests understanding of emission and absorption spectra. Neon atoms have electrons in quantized energy levels, meaning electrons can only occupy specific, discrete energy states. When excited electrons transition from higher to lower energy levels, they emit photons with energies equal to the difference between those levels, producing sharp spectral lines at specific wavelengths. Each transition corresponds to a specific color in the neon sign's glow. Choice A incorrectly suggests energy levels vary continuously, which would produce a continuous spectrum rather than discrete lines. Remember that discrete spectral lines are direct evidence of quantized atomic energy levels.

Question 17

1. Atoms absorb only photons whose energies match transitions between discrete electron energy levels. (correct answer)
2. The absorbed wavelengths are determined by the intensity distribution of the incoming light.
3. Atoms absorb photons of any energy, but only certain wavelengths are blocked by reflection.
4. Electrons emit photons during absorption, so only a few wavelengths are removed.

Explanation: This question tests understanding of emission and absorption spectra. Atoms have electrons in quantized energy levels, and they can only absorb photons whose energies exactly match the energy difference between two allowed levels. When a photon with the correct energy encounters an atom, it can be absorbed, promoting an electron to a higher energy level and removing that wavelength from the transmitted light. Photons with energies that don't match any allowed transition pass through unaffected. Choice B incorrectly suggests atoms can absorb any energy, which would create continuous absorption rather than selective absorption at specific wavelengths. The fundamental principle is that spectral lines correspond to specific energy differences between quantized levels.

Question 18

1. Electrons emit photons during absorption, so the missing wavelengths correspond to emitted photons leaving the beam.
2. Photons are removed based on their intensity, so the weakest colors disappear as dark lines.
3. Energy levels are continuous, but collisions remove photons at random wavelengths that appear as lines.
4. Only photons with energies matching allowed energy-level differences are absorbed to raise electrons to higher levels. (correct answer)

Explanation: This question tests understanding of emission and absorption spectra. Cool gas atoms in their ground or low-energy states can absorb photons from the background continuum source, but only if the photon energies exactly match allowed transitions to higher energy levels. Photons with other energies pass through unaffected because they cannot cause any allowed transitions. This selective absorption creates dark lines at specific wavelengths in the otherwise continuous spectrum. Choice D incorrectly suggests electrons emit photons during absorption, which would violate energy conservation. The key insight is: absorption is wavelength-selective because only photons matching energy-level differences can be absorbed.

Question 19

1. The spectrum is discrete because atomic energy levels are continuous, but only certain intensities can be detected.
2. The spectrum is discrete because electrons emit energy while absorbing photons, limiting the possible emitted intensities.
3. The spectrum is discrete because higher intensity light creates larger gaps between energy levels in the atom.
4. The spectrum is discrete because electrons transition between quantized energy levels, fixing photon energies, not intensities. (correct answer)

Explanation: This question tests understanding of emission and absorption spectra. The student confuses intensity (brightness) with energy (color/wavelength). Emission spectra are discrete because electrons transition between quantized energy levels, producing photons with specific energies and thus specific wavelengths/colors. The intensity of a line indicates how many photons are emitted, not their energy. Choice D incorrectly suggests intensity affects energy-level spacing, mixing up these distinct concepts. The crucial distinction is: spectral lines are discrete in wavelength/energy due to quantization, while intensity varies with the number of atoms emitting.

Question 20

1. Electrons can have any energy, but they radiate only at certain preferred wavelengths set by intensity.
2. Electrons emit photons when they absorb energy, producing a few discrete wavelengths instead of a continuum.
3. Electrons occupy quantized energy levels, so photon energies correspond to specific transitions between levels. (correct answer)
4. The gas emits continuously, but the spectroscope blocks most wavelengths, leaving only a few visible lines.

Explanation: This question tests understanding of emission and absorption spectra. Hot gas atoms have electrons in various excited states due to thermal collisions. These electrons occupy specific quantized energy levels, and when they drop to lower levels, they emit photons with energies equal to the differences between those levels. Since only certain energy differences are allowed, only discrete wavelengths appear, creating a line spectrum rather than a continuum. Choice D incorrectly claims electrons emit photons when absorbing energy, confusing the emission process with absorption. The fundamental principle is: quantized energy levels produce discrete spectral lines, while continuous energy distributions produce continuous spectra.