Hello, I hope you are doing well

Modern physics is a branch of physics which deals with the post-Newtonian concepts in the world of physics. It is based on the two major breakthroughs of the twentieth century Relativity and Quantum Mechanics.

The topics which are considered as sub topics of modern physics are mentioned below:

• Atomic theory and the evolution of the atomic model in general
• Black-body radiation (https://byjus.com/physics/stefan-boltzmann-constant/)
• Franck–Hertz experiment
• Geiger–Marsden experiment (Rutherford’s experiment)
• Gravitational lensing
• Michelson–Morley experiment
• Photoelectric effect
• Quantum thermodynamics
• Radioactive phenomena in general
• Perihelion precession of Mercury
• Stern–Gerlach experiment
• Wave-particle duality
• Solid

Hope this helps