As shown in the figure, a string of length 'l' holds a small bob of mass 'm' while suspended from a point 'O'. The bob revolves about a vertical line OC passing through the point of suspension on a horizontal circle such that the string always remains inclined to the vertical at an angle 'α'. The angular frequency of revolution will be-
1
\(\sqrt {\frac{g}{{l\cos \alpha }}} \)
2
\(\sqrt {\frac{g}{{l\sin \alpha }}} \)
3
\(\sqrt {\frac{g}{{l\tan \alpha }}} \)
4
\(\sqrt {\frac{g}{{l}}} \)