What are the Rules of Hebrew grammar for kamatz katan?

Answer 1

They rules for Kamatz Katan are complicated, but basically a Kamatz in a closed syllable becomes a Kamatz Katan (though it can be tricky to figure out if a syllable is a closed or open).

More information about Kamatz Katan

The Hebrew of the late centuries BCE and early centuries of the Common Era had a system with five phonemic long vowels /aː eː iː oː uː/ and five short vowels /a e i o u/. In the later dialects of the 1st millennium, phonemic vowel length disappeared, and instead was automatically determined by the context, with vowels pronounced long in open syllables and short in closed ones. However, the previous vowel phonemes merged in various ways that differed from dialect to dialect. In Tiberian Hebrew, which underlies the written system of vowels, short /a/ became [a] (indicated by pataḥ); long /oː/ became [o] (indicated by ḥolam); while /aː/ and /o/ both merged into an in-between sound [ɔ] (similar to the vowel in English "caught"), which was indicated by qamatz. In the Babylonian vocalization, however, short and long variants simply merged, with /a/ and /aː/ becoming [a], while /o/ and /oː/ became [o]; and this system underlies the pronunciation of Modern Hebrew.

The result is that the vowel written with kamatz might be pronounced as either [a] or [o], depending on historical origin. It is often said that the two sounds can be distinguished by context:

The kamatz sound of [o], known as Kamatz Kaṭan (קָמַץ קָטָן, "small kamatz") occurs in a "closed syllable", i.e. one which ends in a consonant marked with a shwa nakh (zero vowel) or with a dagesh ḥazaq (which indicates that the consonant was pronounced geminated, i.e. doubled).

The kamatz sound of [a], known as kamatz gadol occurs in an "open syllable", i.e. any other circumstance: one which ends in a consonant followed by a normal vowel, a consonant at the end of a word and with no vowel marking, or a consonant marked with a shwa na (originally pronounced [ǝ]).

Unfortunately, the two varieties of shwa are written identically, and pronounced identically in Modern Hebrew; as a result, there is no reliable way to distinguish the two varieties of kamatz when followed by a vowel marked with a shwa. (In some cases, Biblical texts are marked with a metheg or other cantillation mark that helps to indicate which pronunciation is intended, but this usage is not consistent, and in any case such marks are absent in non-Biblical texts.)

An example of the kamatz katan is the Modern Hebrew word תָּכְנִית‎ ("program").

Answer 2

They rules for Kamatz Katan are complicated, but basically a Kamatz in a closed syllable becomes a Kamatz Katan (though it can be tricky to figure out if a syllable is a closed or open).
More information about Kamatz Katan
The Hebrew of the late centuries BCE and early centuries of the Common Era had a system with five phonemic long vowels /aː eː iː oː uː/ and five short vowels /a e i o u/. In the later dialects of the 1st millennium, phonemic vowel length disappeared, and instead was automatically determined by the context, with vowels pronounced long in open syllables and short in closed ones.

However, the previous vowel phonemes merged in various ways that differed from dialect to dialect. In Tiberian Hebrew, which underlies the written system of vowels, short /a/ became [a] (indicated by pataḥ); long /oː/ became [o] (indicated by ḥolam); while /aː/ and /o/ both merged into an in-between sound [ɔ] (similar to the vowel in English "caught"), which was indicated by qamatz. In the Babylonian vocalization, however, short and long variants simply merged, with /a/ and /aː/ becoming [a], while /o/ and /oː/ became [o]; and this system underlies the pronunciation of Modern Hebrew.

The result is that the vowel written with kamatz might be pronounced as either [a] or [o], depending on historical origin. It is often said that the two sounds can be distinguished by context:
The kamatz sound of [o], known as Kamatz Kaṭan (קָמַץ קָטָן, "small kamatz") occurs in a "closed syllable", i.e. one which ends in a consonant marked with a shwa nakh (zero vowel) or with a dagesh ḥazaq (which indicates that the consonant was pronounced geminated, i.e. doubled).

The kamatz sound of [a], known as kamatz gadol occurs in an "open syllable", i.e. any other circumstance: one which ends in a consonant followed by a normal vowel, a consonant at the end of a word and with no vowel marking, or a consonant marked with a shwa na (originally pronounced [ǝ]).

Unfortunately, the two varieties of shwa are written identically, and pronounced identically in Modern Hebrew; as a result, there is no reliable way to distinguish the two varieties of kamatz when followed by a vowel marked with a shwa. (In some cases, Biblical texts are marked with a metheg or other cantillation mark that helps to indicate which pronunciation is intended, but this usage is not consistent, and in any case such marks are absent in non-Biblical texts.)

An example of the kamatz katan is the Modern Hebrew word תָּכְנִית‎ ("program").