Question

I have noticed that some aayaat of the Qur'an end with a word which has a tanween (double fathah sign ) on the end of it.  Listening to tapes I can hear that the reciter is saying an elongated "aa" .  Could you please explain this?

Answer

When stopping on a word that has a tanween fat-hah, we substitute and alif for the tanween, and there is therefore a two vowel count to this substituted alif.  This is called , which means substitution lengthening. An example of this is found when stopping on the last word of the first ayaah of An-Naazi’aat:
In this above case, we would stop on the last word with an alif, and that alif gets two vowel counts of timing.  

Words that end with the female , also called , and have a tanween fat-hah do not have this substitution when stopping.  These words are instead stopped on with a  saakinah.  An example of this is in the word: .  As stated, we do not stop on this word with a substituted alif, but with a  saakinah.