I have a question concerning the tarqiq or tafkhim of strong letters when they are sakinah depending on the preceding vowel.

Question
Assalamu `alaykum wa rahmatullahi wa barakatuhu

I have a question concerning the tarqiq or tafkhim of strong letters when they are sakinah depending on the preceding vowel.

For example, would the khaa' in "wa-khtilaf" be pronounced differently from the khaa' in "ikhwan"? And would the saad in "islawha" be pronounced differently from the saad in "fa-sbiru"?

And are qalqalah letters always pronounced the same in a sakinah state? For example, is the taa' in "Lut" pronounced the same as the taa' in "muheet"? And would the qaaf in "wariq" be pronounced the same as the qaaf in "dhuq".

Jazakumullahu khayran.

Wassalamu `alaykum

Answer
Wa alaikum assalaam wa rahmatullahi wa barakatuh

There are two different schools of thought in the strength of tafkheem letters.  Both schools of thought are widely accepted by the scholars of tajweed, and in fact there are lines of poetry which describe both schools.
One of the two schools of thought has five levels of tafkheem while the other has three levels.  The five level school of thought has one special category for the saakin letter of  group, while the three level school of thought is such that the saakin letter of the group follows whatever level the vowel is on the letter before the saakin letter of the group .  So, either the level of tafkheem is constant for a saakin letter in the group, or it changes according to the vowel on the letter preceding it. 
These two schools have been described in details in the follow lesson.  Please click on the link below and scroll down a little bit:

http://www.abouttajweed.com/tafkheem-and-tarqeeq/tafkheem-and-tarqeeq-part-1.html

Wa iyyaakum,
Wa assalaam alaikum wa rahmatullah.