What is Eccentricity?

Let’s discuss eccentricity definition, eccentricity formula, eccentricity of circle, eccentricity of parabola, eccentricity of ellipse and eccentricity of hyperbola

• Eccentricity definition – Eccentricity can be defined how much a conic section (a circle, ellipse, parabola or hyperbola) actually varies from being circular.

• A circle has an eccentricity equal to zero, so the eccentricity shows you how un – circular the given curve is. Bigger eccentricities are less curved.

Different Values of Eccentricity Make Different Curves:

[Image will be Uploaded Soon]            

Eccentricity is often represented as the letter (Keep in mind you don’t confuse this with Euler’s number E, they are totally different).

Calculating the value of eccentricity (Eccentricity Formula):

Eccentricity Definition

In Mathematics, for any conic section, there is a locus of a point in which the distances to the point (focus) and the line (known as the directrix) are in a constant ratio. This ratio is referred to as eccentricity and it is denoted by the symbol “e”.

Eccentricity Formula

The formula to find out the eccentricity of any conic section can be defined as

Eccentricity, Denoted by e = \[\frac{c}{a}\]  

Where,

c is equal to the distance from the centre to the focus

a  is equal to the distance from the centre to the vertex

So we can say that for any conic section, the general equation is of the quadratic form:

Ax2 + Bxy + Cy2 + Dx + Ey + F and this equation equals zero.

Now let us discuss the eccentricity of different conic sections namely parabola, ellipse and hyperbola in detail.

Eccentricity of Circle

• A circle can be defined as the set of points in a plane which are equidistant from a fixed point in the plane surface which is known as the “centre”. 

• Now, you might think what is radius. The term “radius” is used to define the distance from the centre and the point on the circle. 

•  If the centre of the circle is at the origin, it becomes easy to derive the equation of a circle. 

We can derive the equation of the circle is derived using the below-given conditions.

In a given circle if “r’ is equal to the radius and C (h, k) is equal the centre of the circle, then by the definition of circle and eccentricity , we get,

 | CP | = radius(r)

We know that the formula to find the distance is,

√[(x –h)2+( y–k)2]= radius(r)

Taking Square on both the sides, we get the following equation,

(x –h)2+( y–k)2= radius2

Thus, the equation of the circle with centre C (h, k) and radius equal to “r” can be written as (x –h)2+( y–k)2= r2

Also, e = 0 for a circle.

Eccentricity of Parabola

• A parabola in mathematics is defined as the set of points P in which the distances from a fixed point F (focus) in the plane are equal to their distances from a fixed-line l(directrix) in the plane. 

• In other words, we can say that the distance from the fixed point in a plane bears a constant ratio equal to the distance from the fixed-line in a plane.

Therefore, the eccentricity of the parabola is always equal to1 ( e=1)

The general equation of a parabola can be written as x2 = 4ay and the eccentricity is always  given as 1.

Eccentricity of Ellipse

• An ellipse can be defined as the set of points in a plane in which the sum of distances from two fixed points is constant. 

• In simple words, the distance from the fixed point in a plane bears a constant ratio less than the distance from the fixed-line in a plane.

Therefore, the eccentricity of the ellipse is less than 1. i.e., e < 1

The general equation of an ellipse is denoted as \[\frac{\sqrt{a²-b²}}{a}\]  

For an ellipse,  the values a and b are the lengths of the semi-major and semi-minor axes respectively.

Eccentricity of Hyperbola

• A hyperbola is defined as the set of all points in a plane where the difference of whose distances from two fixed points is constant. 

• In simpler words, the distance from the fixed point in a plane bears a constant ratio greater than the distance from the fixed-line in a plane.

Therefore, the eccentricity of the hyperbola is always greater than 1. i.e., e > 1

The general equation of a hyperbola is denoted as \[\frac{\sqrt{a²+b²}}{a}\] 

For any hyperbola, the values a and b are the lengths of the semi-major and semi-minor axes respectively

Questions to be Solved:

Question 1) List down the formulas for calculating the eccentricity of hyperbola and parabola.

Answer) 

For a hyperbola, the value of eccentricity is: \[\frac{\sqrt{a²+b²}}{a}\] 

For an ellipse, the value of eccentricity is equal to: \[\frac{\sqrt{a²-b²}}{a}\]