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.
The amplitude determines the loudness of a sound wave.
It is the frequency of a sound that determines its pitch. The higher the frequency, the higher the pitch.
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.
Amplitude of a sound wave determines LOUDNESS.
the pitch of the sound.
It determines how loud or soft the sound is.
The pich of a sound is the perception of its freqency.
The keynote
the intesity of sound
We perceive the loudness of a sound wave as a consequence of its amplitude. The frequency of a sound wave determines the pitch we perceive.