--- title: "Paschen Series in College Physics I" description: "Paschen series is the set of hydrogen spectral lines made when electrons drop to n = 3, producing infrared light in College Physics I." canonical: "https://fiveable.me/intro-college-physics/key-terms/paschen-series" type: "key-term" subject: "College Physics I – Introduction" unit: "Unit 30" --- # Paschen Series in College Physics I ## Definition The Paschen series is the set of hydrogen emission lines created when an electron falls from a higher energy level to n = 3. In College Physics I, it shows up as an infrared part of Bohr's quantized hydrogen spectrum. ## What It Is The Paschen series is the group of hydrogen spectral lines you get when an electron drops from any higher level down to the n = 3 energy level. In College Physics I, that makes it one of the named hydrogen emission series in Bohr’s model, alongside the Lyman and Balmer series. Each line in the series comes from a different starting level. The first Paschen line, called Paschen-alpha, is the transition n = 4 to n = 3. Other lines come from n = 5, 6, 7, and so on, all landing on n = 3. Because the energy gap gets smaller as the starting level gets higher, the wavelengths in the series get closer together. These lines are in the infrared region of the electromagnetic spectrum, not visible light. That matters because hydrogen does not just emit one color of light, it emits specific wavelengths tied to specific energy changes. The Paschen series sits at longer wavelengths than the visible Balmer lines, so you would not see it with your eyes, but it is still part of hydrogen’s emission spectrum. The pattern comes from quantized energy levels in Bohr’s model. Electrons can only occupy certain stationary states, and when an electron moves between them, the atom emits a photon whose energy matches the difference between the two levels. For Paschen transitions, the emitted photon has exactly the energy needed to end at n = 3. You can calculate the wavelength with the Rydberg formula for hydrogen. In practice, that means if a problem gives you a transition like n = 6 to n = 3, you identify the final level, recognize the series as Paschen, and use the energy difference or Rydberg equation to find the emitted infrared wavelength. ## Why It Matters Paschen series is one of the cleanest examples of how Bohr’s quantized energy levels show up in real data. Instead of treating light emission as continuous, College Physics I uses this series to show that hydrogen produces only certain wavelengths, and those wavelengths line up with specific electron transitions. That connection gives you a way to move between a diagram and a physical result. If you see a level diagram with arrows ending at n = 3, you can identify the series immediately. If you see a wavelength or photon-energy problem, you can work backward to the transition that produced it. It also reinforces a big idea in atomic physics: the final energy level determines the series name. Lyman ends at n = 1, Balmer ends at n = 2, and Paschen ends at n = 3. Once you know that pattern, spectra questions become much easier to sort out. In lab or class discussion, this term often comes up when you compare visible and infrared radiation. The Paschen series is a simple reminder that not all atomic emission is visible, and instruments can detect light far beyond the range of human vision. ## Connections ### Hydrogen Atom The Paschen series is a hydrogen spectrum pattern, so it only makes sense in the context of the hydrogen atom’s single electron. Hydrogen is the simplest atom to analyze with Bohr’s model, which is why its spectral lines are used so often in introductory physics. If you understand hydrogen’s level structure, the Paschen series becomes a direct readout of electron transitions. ### Emission Spectrum Paschen lines are part of hydrogen’s emission spectrum, meaning they are photons emitted when the atom loses energy. The series is a good example of why emission spectra are line spectra instead of continuous rainbows. Each visible or infrared line corresponds to one allowed transition, not any random wavelength. ### [Balmer series](/intro-college-physics/key-terms/balmer-series) Balmer series is the closest comparison because it is the hydrogen series many students meet first. Balmer transitions end at n = 2 and mostly fall in the visible range, while Paschen transitions end at n = 3 and fall in the infrared. Comparing the two helps you see how the final energy level changes the wavelength range. ### [Stationary States](/intro-college-physics/key-terms/stationary-states) Paschen transitions only happen because electrons are allowed to occupy certain stationary states in Bohr’s model. The electron is not spiraling down continuously, it stays in one state until a transition occurs. The Paschen series is the evidence that those states are discrete and that the atom emits light in specific jumps. ## On the AP Exam A quiz or problem set may ask you to identify which series a transition belongs to, or to calculate the wavelength of a hydrogen line from n = 5 to n = 3. The move is to look at the final level first, since n = 3 means Paschen series no matter where the electron started. You might also label a spectrum diagram and decide whether a line is infrared, visible, or ultraviolet based on the transition. If the question gives a wavelength range or asks for the first line, you connect Paschen-alpha to n = 4 to n = 3. In short, you use the term to classify transitions, interpret level diagrams, and match energy changes to spectral lines. ## Paschen series vs Balmer series Paschen series and Balmer series are easy to mix up because both are hydrogen emission series named after the final energy level. The difference is the destination level: Paschen ends at n = 3 and gives infrared light, while Balmer ends at n = 2 and gives mostly visible light. If a problem asks for a hydrogen line in the infrared, Paschen is usually the one to check first. ## Key Takeaways - The Paschen series is the set of hydrogen emission lines created when an electron falls to n = 3. - These transitions produce infrared light, so you cannot see Paschen lines with your eyes even though they are real spectral features. - Paschen-alpha is the first line in the series, and it comes from the n = 4 to n = 3 transition. - The series is a direct example of quantized energy levels in Bohr’s model, where each emitted photon matches one specific energy drop. - When you solve hydrogen problems, the final level tells you the series name before you do any calculation. ## FAQs ### What is the Paschen series in College Physics I? The Paschen series is the set of hydrogen spectral lines formed when an electron drops from a higher energy level to n = 3. In College Physics I, it is used as evidence that hydrogen emits light in discrete wavelengths rather than continuously. These lines are in the infrared region. ### Is the Paschen series visible light? No, the Paschen series is infrared, so it lies outside the visible range. That is one reason it is different from the Balmer series, which sits mostly in visible light. You usually identify Paschen lines through wavelength calculations or spectral data, not by eye. ### What is Paschen-alpha? Paschen-alpha is the first line in the Paschen series. It comes from the transition n = 4 to n = 3 in a hydrogen atom. On a problem, if you see Paschen-alpha, you know the electron ended at n = 3. ### How do I tell Paschen series from Balmer series? Check the final energy level. Paschen transitions end at n = 3, while Balmer transitions end at n = 2. That difference changes the wavelength range too, with Paschen in the infrared and Balmer mostly in the visible. ## Related Study Guides - [30.3 Bohr’s Theory of the Hydrogen Atom](/intro-college-physics/unit-30/3-bohrs-theory-hydrogen-atom/study-guide/tQHuZbcrrmatFHH9) ## About This Document Canonical Fiveable pages are available as Markdown at the same path plus `.md`. - [llms.txt](https://fiveable.me/llms.txt): index of Fiveable's sections and URL patterns - [llms-full.txt](https://fiveable.me/llms-full.txt): complete subject and unit listing - [MCP server](https://fiveable.me/mcp): call Fiveable as tools instead of fetching pages (`https://fiveable.me/api/mcp`) - [MCP server for AP teachers](https://fiveable.me/mcp/teachers): a teacher's classes, assignments and AP-rubric grading (`https://fiveable.me/api/mcp/teacher`) ## Structured Data ```json {"@context":"https://schema.org","@graph":[{"@type":"LearningResource","@id":"https://fiveable.me/intro-college-physics/key-terms/paschen-series#resource","name":"Paschen Series in College Physics I","url":"https://fiveable.me/intro-college-physics/key-terms/paschen-series","learningResourceType":"Concept explainer","educationalLevel":"AP® / High School","about":{"@id":"https://fiveable.me/intro-college-physics/key-terms/paschen-series#term"},"audience":{"@type":"EducationalAudience","educationalRole":"student"},"dateModified":"2026-07-03T02:22:15.477Z","isPartOf":{"@type":"Collection","name":"College Physics I – Introduction Key Terms","url":"https://fiveable.me/intro-college-physics/key-terms"},"author":{"@type":"Organization","@id":"https://fiveable.me/editorial#content-team","name":"Fiveable Content Team","url":"https://fiveable.me/editorial","parentOrganization":{"@id":"https://fiveable.me/#organization"},"member":[{"@type":"Person","name":"Amanda DoAmaral","sameAs":["https://www.linkedin.com/in/adoamaral"]},{"@type":"Person","name":"Becky Bahr","sameAs":["https://www.linkedin.com/in/becky-bahr-b52743132"]}]},"publisher":{"@type":"Organization","name":"Fiveable","url":"https://fiveable.me"}},{"@type":"DefinedTerm","@id":"https://fiveable.me/intro-college-physics/key-terms/paschen-series#term","name":"Paschen series","description":"The Paschen series is the set of hydrogen emission lines created when an electron falls from a higher energy level to n = 3. 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