ming, The meaning of "pH" is "potential of hydrogen" -- a chemistry term. The "H" in pH is capitalized because the symbol for hydrogen is capital H. Translating that into a useful pH definition, there is a pH scale that reflects how powerful or weak the Hydrogen particles are in a solution.

Just a whim :P

If we write pH you are referring to the measurement of a specific atom . Now is you write ph it's a degree depending on the letter you put in front to the p for example ph.B OR ph.C and many more.