Notes On Sphere and Hemisphere - CBSE Class 9 Maths
A sphere is a three dimensional figure, made up of points that are equidistant from a given point. It does not have an edge or a vertex. The surface of a sphere is uniform and smooth. The centre of a sphere is a point, which is equidistant from all the points on the sphere. The distance between the centre and any point on the surface of the sphere is called the radius of the sphere. Generally the radius is denoted by the letter r. A line segment through the centre of the sphere, and with the end points on the sphere is called a diameter of the sphere. Surface area of a sphere (A) = 4πr2 Volume of a sphere (V) = $\frac{\text{4}}{\text{3}}$ πr3   A plane through the centre of a sphere divides the sphere into two equal parts, each of which is called a hemisphere. A hemisphere has two faces. A flat surface which is called as the base and a curved surface. Surface area of a hemisphere = 2πr2 Total surface area of a hemisphere = 3πr2   Volume of a hemisphere = $\frac{\text{2}}{\text{3}}$πr3

#### Summary

A sphere is a three dimensional figure, made up of points that are equidistant from a given point. It does not have an edge or a vertex. The surface of a sphere is uniform and smooth. The centre of a sphere is a point, which is equidistant from all the points on the sphere. The distance between the centre and any point on the surface of the sphere is called the radius of the sphere. Generally the radius is denoted by the letter r. A line segment through the centre of the sphere, and with the end points on the sphere is called a diameter of the sphere. Surface area of a sphere (A) = 4πr2 Volume of a sphere (V) = $\frac{\text{4}}{\text{3}}$ πr3   A plane through the centre of a sphere divides the sphere into two equal parts, each of which is called a hemisphere. A hemisphere has two faces. A flat surface which is called as the base and a curved surface. Surface area of a hemisphere = 2πr2 Total surface area of a hemisphere = 3πr2   Volume of a hemisphere = $\frac{\text{2}}{\text{3}}$πr3

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