Circles, ellipses, parabolas and hyperbolas are known as conic sections because they can be obtained as intersections of a plane with a double napped right circular cone.
These curves have a very wide range of applications in fields such as planetary motion, design of telescopes and antennas, reflectors in flashlights and automobile headlights, Projectile motion, sand clock, Ball etc
When Ф = θ , the section is ellipse.
when ø = 90' the section is circle.
when θ < ø < 90' the section is an ellipse.
when 0 ≤ θ ≤ ø the plane cut through both the nappes and the curves of intersection is a hyperbola.