How the ideas connect
A good science page should make the connection visible, not just list definitions.
Spectroscopy
Spectroscopy studies how matter emits, absorbs or scatters electromagnetic radiation as a function of wavelength, frequency or energy.
Spectra act like structured fingerprints: their lines and bands reveal energy levels, composition and molecular structure.
Atomic spectra
Atomic emission and absorption spectra contain discrete lines because atoms exchange photons whose energies match differences between quantized energy states.
Spectral lines provide a direct experimental bridge between quantum energy levels and the chemical identity of an element.
Photoelectric effect
In the photoelectric effect, electrons are emitted from a material when incident electromagnetic radiation has sufficiently high photon energy.
Increasing intensity raises the number of available photons, but below the threshold frequency it does not compensate for insufficient photon energy.
Blackbody radiation
An ideal blackbody absorbs all incident radiation and emits a characteristic thermal spectrum determined by its temperature.
The spectrum shifts and strengthens as temperature rises, providing a bridge between thermodynamics, electromagnetism and quantum physics.
What to notice
A good science page should make the connection visible, not just list definitions.
Sources
IUPAC Gold Book · NIST · BIPM