The words incidence, incidents sound the same but have different meanings and spellings. Why do incidence, incidents sound the same even though they are completely different words?
The answer is simple: incidence, incidents are homophones of the English language.
The act or an instance of happening; occurrence: did not expect criticism and was surprised by its incidence.
Extent or frequency of occurrence: a high incidence of malaria in the tropics.
Physics The arrival of radiation or a projectile at a surface.
Physics Angle of incidence.
Plural form of incident.
Definitions from The American Heritage® Dictionary of the English Language, 4th Edition, from Wiktionary, Creative Commons Attribution/Share-Alike License and Wordnik.
Homophones (literally "same sound") are usually defined as words that share the same pronunciation, regardless of how they are spelled.