Concept Explanations

Atomic, Nuclear, and Particle Physics

7.1 – Discrete Energy and Radioactivity

7.1.1 – Energy Levels in an Atom

7.1.2 – Emission Spectra

7.1.3 – Absorption Spectra

7.1.4 – Radioactive Decay

7.1.5 – Half-life

Definitions to Memorize*








Emission Spectrum Formation
  • Electrons in the gas atoms move from higher to lower energy levels and emit photons.
  • Since energy levels in the atom are discrete, the emitted photons have specific, discrete frequencies.
  • Photons having these discrete frequencies result in the emission spectrum seen for the gas.

Video 7.1.3

Radioactive Decay
  • is random, because it is impossible to predict when a particular nuclide will decay.
  • is spontaneous, because it is impossible to influence or modify the decay in any way.

Video 7.1.5


* The terms and concepts above have directly come up on past IB Physics exams from May 2016 onwards. 

Directly in this context  means that the answer to a Paper 1 or Paper 2 question was the definition of the term or concept or that the answer could be deduced directly from the definition.  Therefore, this list might be helpful when you are deciding what to memorize for your IB Physics exams.

To see a complete list of definitions from all topics along with the number of times the term/concept occured on exams since May 2016, click on the link below:

All Definitions from Past IB Exams (pdf)

Topic Specific PaperPlainz Resources

SL Questionbank

Atomic, Nuclear, and Particle Physics

Full Membership
SL Past Exam Video Solutions by Topic

Atomic, Nuclear, and Particle Physics

Full Membership

Sub-topic 7.2 →