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 The Effect of Air Gap Width (S) and the Ratio (P1/D2) on .Minimum Projector Focal Length (Fp)min  for the Double Pole-Piece Lens- at Costant Excitation (NI).
<strong>Ibn AL- Haitham Journal For Pure and Applied Science</strong>, [S.l.], v. 21, n. 3, p. 95-111, sep. 2017.
ISSN 2521-3407.
Available at: &lt;<a href="http://jih.uobaghdad.edu.iq/index.php/j/article/view/1412" target="_new">http://jih.uobaghdad.edu.iq/index.php/j/article/view/1412</a>&gt;. Date accessed: 22 nov. 2019.