Letter	Sub heading
A	Physics generally
B	History and philosophy of physics
C	Mathematics in relation to physics
D	Geophysics
E	Astrophysics, space physics
F	Space research, astrodynamics
G	Cosmology, relativity and gravity
J	Properties of matter
K	Acoustics
L	Optics
M	Heat
N	Electricity and magnetism
P	Atomic and molecular structure
Q	Nuclear and high-energy physics
R	Quantum mechanics
S	Medical physics
T	Technology for physicists