The eccentricity of the ellipse whose major axis is three times the minor axis is:
- $\frac{\sqrt{2}}{3}$
- $\frac{\sqrt{3}}{2}$
- $\frac{2\sqrt{2}}{3}$
- $\frac{2}{\sqrt{3}}$
The Correct Option is C
Solution and Explanation
Eccentricity is given by :
$b^{2} = a^{2}\left(1 - e^{2}\right)$
$\Rightarrow b^{2} = 9b^{2}\left(1 - e^{2}\right)$
$\Rightarrow \frac{1}{9} = \left(1 - e^{2}\right) \Rightarrow e^{2} = \frac{8}{9} \Rightarrow e = \frac{2\sqrt{2}}{3}$
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Concepts Used:
Ellipse
Ellipse Shape
An ellipse is a locus of a point that moves in such a way that its distance from a fixed point (focus) to its perpendicular distance from a fixed straight line (directrix) is constant. i.e. eccentricity(e) which is less than unity
Properties
- Ellipse has two focal points, also called foci.
- The fixed distance is called a directrix.
- The eccentricity of the ellipse lies between 0 to 1. 0≤e<1
- The total sum of each distance from the locus of an ellipse to the two focal points is constant
- Ellipse has one major axis and one minor axis and a center
Read More: Conic Section
Eccentricity of the Ellipse
The ratio of distances from the center of the ellipse from either focus to the semi-major axis of the ellipse is defined as the eccentricity of the ellipse.
The eccentricity of ellipse, e = c/a
Where c is the focal length and a is length of the semi-major axis.
Since c ≤ a the eccentricity is always greater than 1 in the case of an ellipse.
Also,
c2 = a2 – b2
Therefore, eccentricity becomes:
e = √(a2 – b2)/a
e = √[(a2 – b2)/a2] e = √[1-(b2/a2)]
Area of an ellipse
The area of an ellipse = πab, where a is the semi major axis and b is the semi minor axis.
Position of point related to Ellipse
Let the point p(x1, y1) and ellipse
(x2 / a2) + (y2 / b2) = 1
If [(x12 / a2)+ (y12 / b2) − 1)]
= 0 {on the curve}
<0{inside the curve}
>0 {outside the curve}