Long Vowels in English

[ɑ:]

The sound is formed in the larynx.
In writing it is expressed by letter  "a" and letter combination "ar" in stressed position.

a - rather ['rɑːðə] 
ar - garden ['gɑːd(ə)n] 
ar - departure [dɪ'pɑːʧə] 

[i:]

It is pronounced with the lips stretched. In writing it is referred to by letters "e", "i" and letter combinations "ee", "ea", "ie", "ei" in the stressed syllable, sometimes by "ey" at the end of the word. 

e - scene [siːn] 
i - magazine [ˌmægə'ziːn] 
ee - beet [biːt] 
ea - clean [kliːn] 
ie - niece [niːs] 
ei - receipt [rɪ'siːt] 
ey - key [kiː] 

[ɔ:]

The lips are protruded and rounded when You pronounce this long vowel.
In writing it can be expressed by letter "a" before "l" or "ll", as well as by letter combinations "or", "aw" and "au".

a - call [kɔːl] 
or - form [fɔːm] 
aw - straw [strɔː] 
au - author ['ɔːθə] 

[u:]

It is expressed by letters "u" and "o", as well as by letter combinations "oo", "ou", "oe", "ue", "ew", "ough". The lips are a little protruded but not rounded.

u - ruler ['ruːlə] 
o - do [duː] 
oo - mood [muːd] 
ou - routine [ruː'tiːn] 
oe - shoe [ʃuː] 
ue - blue [bluː] 
ew - brew [bruː] 
ough - through [θruː] 

[ɜː]

Long neutral sound, one of the most complicated in English. The lips are stretched. In writing it is expressed by letter combinations "ir", "ur", "er" in a stressed syllable, as well as by "or", "ear".

ir - stir [stɜː] 
ur - burn [bɜːn] 
er - person ['pɜːs(ə)n] 
or - worth [wɜːθ] 
ear - learn [lɜːn]