Photon — Science definition

Defined in 2 courses:

Where it is taught

In use

An excited state is less stable; a transition to a lower state can release a photon with energy equal to the difference between states.

Electron Transitions & Emission Spectra

A dim blue light can free electrons that an intense red light cannot, because what matters is the energy per photon, set by frequency, not the total brightness.

Light & the Electromagnetic Spectrum

Questions using photon

Problem 1

Find photon energy for f=5.0×10¹⁴ Hz using h=6.63×10⁻³⁴ J·s. Show the reasoning, not just the conclusion.
Hints

Emission lowers atomic energy; absorption raises it.

Answer and explanation

E=hf=3.315×10⁻¹⁹ J, about 3.3×10⁻¹⁹ J.

Problem 2

A selected atom has levels at 0, 1.5 and 4.5 eV. Find the energy and approximate vacuum wavelength for a 4.5-to-1.5 eV emission. Could a further drop emit another photon?
Answer and explanation

The first photon has 3.0 eV, or about 4.81×10⁻¹⁹ J, giving λ≈4.14×10⁻⁷ m =414 nm. A later allowed 1.5-to-0 transition could emit a 1.5 eV photon; the selected model does not supply transition probabilities.

The first photon has 3.0 eV, or about 4.81×10⁻¹⁹ J, giving λ≈4.14×10⁻⁷ m =414 nm. A later allowed 1.5-to-0 transition could emit a 1.5 eV photon; the selected model does not supply transition probabilities.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the chemical mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Problem 3

Independent chapter check: A selected atom has levels at 0, 1.5 and 4.5 eV. Find the energy and approximate vacuum wavelength for a 4.5-to-1.5 eV emission. Could a further drop emit another photon?
Answer and explanation

The first photon has 3.0 eV, or about 4.81×10⁻¹⁹ J, giving λ≈4.14×10⁻⁷ m =414 nm. A later allowed 1.5-to-0 transition could emit a 1.5 eV photon; the selected model does not supply transition probabilities.

The first photon has 3.0 eV, or about 4.81×10⁻¹⁹ J, giving λ≈4.14×10⁻⁷ m =414 nm. A later allowed 1.5-to-0 transition could emit a 1.5 eV photon; the selected model does not supply transition probabilities.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the chemical mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Problem 4

A photon has a frequency of 1 × 10¹⁵ Hz. Using h = 6.63 × 10⁻³⁴ J·s, find its energy in joules.
Answer and explanation

6.63e-19 J

E = h f = (6.63 × 10⁻³⁴) × (1 × 10¹⁵) = 6.63 × 10⁻¹⁹ J.

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