As in much of English there is no rule.
There has been a story doing the rounds here in England about an English teacher trying to teach just this to a class. She stated quite categorically that ch was always either ch as in church or k as in mechanic.
One little girl put up her hand and said "Sometimes it's a 'sh' sound Miss".
The teacher said "No it's not Charlotte".
See also ricochet, chevron and others.
/ch/ will make the "k" sound when in a consonant blend (ex. school, Christmas, chlorine). Greek origin words also make the "k" sound (ex. character)
The amplitude determines the loudness of a sound wave.
Others are where and who. They are all words that begin with 'wh' and also they begin with the 'h' sound. Some speakers drop the 'h' sound from the first four.
If you write the names of the Hebrew letters in English, then there are the only two letters that begin with A: Alef and Ayin.Note that neither of these letters represent an "A" sound in Hebrew.
It determines how loud or soft the sound is.
Amplitude of a sound wave determines LOUDNESS.
It is the frequency of a sound that determines its pitch. The higher the frequency, the higher the pitch.
The pich of a sound is the perception of its freqency.
the intesity of sound
The keynote
The frequency of a sound wave determines the pitch of the sound, with higher frequencies corresponding to higher pitches and lower frequencies corresponding to lower pitches.
The amplitude of the sound wave determines the volume of sound. Greater amplitude produces louder sounds, while lower amplitude results in softer sounds.
A sound wave consists of three main components: frequency, which determines the pitch of the sound; amplitude, which determines the loudness of the sound; and wavelength, which determines the speed and energy of the wave.