Physics Week 3 Lecture Notes: Atomic Structure, Photoelectric Effect, and Medical Imaging

Vocabulary flashcards covering atomic structure, energy levels, the photoelectric effect, and imaging concepts from Week 3 notes.

Atom

The basic unit of matter consisting of a nucleus (protons and neutrons) with electrons orbiting around it; electrons occupy discrete energy levels.

Nucleus

The central region of an atom containing protons and neutrons.

Proton

Positively charged subatomic particle located in the nucleus.

Neutron

Electrically neutral subatomic particle located in the nucleus.

Electron

Negatively charged subatomic particle orbiting the nucleus; occupies discrete energy levels.

Principal quantum number (n)

Quantum number describing the energy level of an electron; n=1 is the ground state for hydrogen.

Ground state

The lowest energy state of an electron (n=1 for hydrogen).

Energy level

Discrete allowed energies for an electron around a nucleus.

Absorption

Process by which an electron moves to a higher energy level after absorbing a photon with exactly the required energy.

Emission

Process by which an electron drops to a lower energy level and emits a photon with energy equal to the difference.

Photon

A quantum of light carrying energy E = hf corresponding to its frequency.

Hydrogen atom energy En

Energy of level n in a hydrogen atom: En = -13.6 eV / n^2.

Kinetic energy (K)

Energy of motion, K = 1/2 m v^2; increases with the square of velocity.

Photoelectric effect

Emission of electrons from a material when illuminated by light with enough energy (above threshold) to overcome binding energy.

Threshold frequency (f0)

Minimum light frequency required to cause photoelectric emission.

Work function / Binding energy (Ebind)

Energy needed to liberate an electron from a material; also called the binding energy.

Photon energy (Eph)

Energy of a photon, Eph = hf.

Eph = Ebind + K

In the photoelectric effect, the photon energy equals the binding energy plus the kinetic energy of the ejected electron.

X-rays

High-energy photons used in medical imaging; their absorption varies by tissue, contributing to image contrast.

Contrast

How clearly differences between lighter and darker parts of an image are seen.

Spatial resolution

Ability of an imaging technique to display small details and distinguish closely spaced structures.

Voxel

A volumetric pixel; the 3D element used to describe image data in imaging.

Radiography

Imaging technique using X-rays to view internal structures.

CT scans

Computed tomography; 3D imaging obtained from multiple X-ray images taken around an object.

Tissue absorption differences

Variation in X-ray absorption among tissues that creates image contrast.