physics

Lyman–Werner photons

Lyman–Werner photons is a physics topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Lyman–Werner photons rather than just read about it. In short: A Lyman-Werner photon is an ultraviolet photon with a photon energy in the range of 11.2 to 13.6 eV, corresponding to the energy range in which the Lyman and Werner absorption bands of molecular hydrogen (H2) are found. A photon in this energy range, with a frequency that coincides with that of one of the lines in the Lyman or Werner bands, can be absorbed by H2, placing the molecule in an excited electronic state.

Key takeaways

Lyman–Werner photons belongs to physics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Lyman–Werner photons to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Lyman–Werner photons from memory before moving on to harder problems.

Reference excerpt

A Lyman-Werner photon is an ultraviolet photon with a photon energy in the range of 11.2 to 13.6 eV, corresponding to the energy range in which the Lyman and Werner absorption bands of molecular hydrogen (H2) are found. A photon in this energy range, with a frequency that coincides with that of one of the lines in the Lyman or Werner bands, can be absorbed by H2, placing the molecule in an excited electronic state. Radiative decay (that is, decay into photons) from this excited state occurs rapidly, with roughly 15% of these decays occurring into the vibrational continuum of the molecule, resulting in its dissociation. This two-step photodissociation process, known as the Solomon process, is one of the main mechanisms by which molecular hydrogen is destroyed in the interstellar medium.

In reference to the figure shown, Lyman-Werner photons are emitted as described below:

A hydrogen molecule can absorb a far-ultraviolet photon (11.2 eV < energy of the photon < 13.6 eV) and make a transition from the ground electronic state X to excited state B (Lyman) or C (Werner). Radiative decay occurs rapidly. 10–15% of the decays occur into the vibrational continuum. This means that the hydrogen molecule has dissociated. Photo-dissociation fragments carry away some of the photon energy as kinetic energy, heating the gas. Rest of the decays are either radiative decay (infrared emission) or collisional, which ultimately end up heating the gas.

Illustrations

Worked examples

Example 1 — a first encounter with Lyman–Werner photons

Start with the simplest possible case. Write down what Lyman–Werner photons claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Lyman–Werner photons before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Lyman–Werner photons ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Lyman–Werner photons

In research: Lyman–Werner photons appears in physics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Lyman–Werner photons in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Lyman–Werner photons is common in secondary-school and first-year university syllabi. It links to neighbouring topics Astrophysics stubs, Photons, so understanding it makes those chapters shorter.
In everyday life: Look for Lyman–Werner photons outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Lyman–Werner photons in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Lyman–Werner photons means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Lyman–Werner photons out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Lyman–Werner photons in simple terms?

Why does Lyman–Werner photons matter?

Because it connects several physics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Lyman–Werner photons?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Lyman–Werner photons.