He is an expert in physics.

Electromagnetism is a part of physics that studies the interaction between electricity and magnetism.

He is good at solving geometry problems.

He is an expert in toxicology and conducts many studies.

He is an expert in mythology and gave a lecture on the gods of ancient Greece.

He is an expert in bibliography and has many publications.

He is an expert in sociology.

Taxonomy is the science of finding, understanding, and naming species of organisms.

I love biology.

Phonetics is a part of linguistics that studies the physical, physiological, and psychological aspects of sounds.