Lecture Notes: Practice Exams, Photoelectric Effect, and Atomic Models

A set of practice-flashcards covering practice-exam strategy, photon energy relations, the photoelectric effect, unit conversions, and introductory quantized atomic models.

What is the recommended strategy for using practice exams to study for the real exam?

Take the practice exam once, score yourself, then study; focus on understanding underlying principles rather than memorizing individual questions; consider writing your own exam questions and skip very hard items to return to if you have time.

What is the equation that relates a photon's energy to its wavelength?

E = h c / λ, where h is Planck's constant and c is the speed of light in vacuum.

In the photoelectric effect, how is the incoming photon energy distributed when an electron is ejected?

Energy is conserved: Ephoton = φ (work function) + KE of the emitted electron, so KE = Ephoton − φ.

Why do you convert kilojoules per mole to joules per photon when solving a photoelectric problem?

Because the photon-energy equations deal with energy per photon in joules, so you must convert per-mole amounts to per-photon amounts.

How do you convert from energy per mole to energy per photon?

Divide the energy per mole (in joules per mole) by Avogadro's number (after converting to joules if needed) to obtain energy per photon.

Why is it important to track units and use flowcharts when solving these problems?

To ensure consistency (per photon vs per mole) and to guide the calculation steps with correct conversions and sequencing.

What happens to any excess energy of a photon after knocking an electron loose in the photoelectric effect?

It becomes the kinetic energy of the emitted electron.

What is the conceptual view of light discussed in the lecture with respect to photons?

Light can behave as particles called photons; photons have energy that depends on the color (frequency) of light, while all photons travel at the same speed in vacuum.

What is the speed of light in vacuum and how does it relate to photon energy across colors?

Speed of light is approximately 3.0 × 10^8 m/s for all colors; photon energy varies with color (frequency), even though speed is the same.

Why do emission spectra from hydrogen or neon show discrete lines rather than a continuum?

Because energy levels are quantized; electrons can only transition between fixed energy levels, emitting photons with specific energies.

What does the Bohr model propose about electron motion in atoms, and how is it viewed today?

Electrons orbit the nucleus in fixed, quantized orbits (energy levels); the Bohr model is a simplified, largely historical starting point and is not the full correct picture of atomic structure.

How do spectral lines arise in the Bohr model explanation of hydrogen?

From electrons transitioning between energy levels; the energy difference determines the color of the emitted photon, producing discrete lines.

What is the Balmer series and which hydrogen transition is responsible for the red line in the visible spectrum?

The Balmer series involves transitions to n=2; the 3 → 2 transition produces the red Balmer line (H-alpha) in the visible spectrum.

What determines the minimum photon energy required to eject an electron from a metal surface?

The work function φ of the metal; photons with energy below φ do not eject electrons.

Which constants relate energy to frequency and wavelength in photon theory, and what are their roles?

E = h f and E = h c / λ; h is Planck's constant, c is the speed of light; these relate photon energy to frequency and wavelength.

What is a practical approach to solving problems that involve two photon-energy equations and kinetic energy?

Use E = h f or E = h c / λ for photon energy, relate to kinetic energy and work function, and ensure unit consistency and proper conversions between per-photon and per-mole.

What does it mean for energy levels to be quantized, as discussed in the lecture?

Only certain discrete energy values are allowed; transitions occur in jumps between these levels, not in a continuous range.

Why is the Bohr model still discussed even though it is not fully correct?

It provides an intuitive visualization of quantization and explains key spectral features; it serves as a stepping stone to quantum mechanics.

How can you determine the wavelength of a photon if you know its energy?

Use λ = h c / E_photon.

How does ultraviolet (UV) light affect photoelectric emission compared to visible light?

UV light has higher energy photons and can eject electrons with higher kinetic energy; visible light may eject electrons if above threshold energy but with lower KE.

What does the term 'blue line' refer to in the lecture context regarding photoelectric emission?

It indicates the minimum wavelength (highest photon energy) that can knock electrons loose for a given momentum, i.e., the threshold energy path.